At present,China’s agriculture is facing some prominent problems,such as resource shortage,environmental pollution and ecosystem degradation.It is urgent to change to resource-saving and environment-friendly to realize green development of agriculture.Agricultural ecological environment is an important part of green agricultural development,and nitrogen flow and related indicators in agricultural system reflect the changes of agricultural ecological environment.County is the basic unit of national administrative regulation and control,with regional characteristics and complete political and economic functions,is the best unit for the implementation of green agricultural development.In this paper,168 counties(districts)in Hebei Province were selected as the research object,focusing on the agricultural ecological environment and its related elements,a total of 7 agricultural system nitrogen flow indicators and 19 other indicators were selected.Based on expert opinions and statistical data,and referring to the degree of agricultural green development,the selected indicators were divided into grade Ⅰ,Ⅱ,Ⅲ and Ⅳ from high to low,and the agricultural system nitrogen in Hebei Province in 1996 and 2016 was analyzed quantitatively The main characteristics of element flow and related indicators,the main influencing factors of nitrogen flow in agricultural system were explored,and the main ways of nitrogen regulation in agricultural system of Hebei Province were put forward through correlation analysis and index relationship regulation,which provided scientific basis for the improvement of agricultural ecological environment.The main results are as follows:(1)From 1996 to 2016,the agricultural ecological environment of counties in Hebei province gradually deteriorated,and the ecological environment risk was still at a high level.Compared with 1996,the results of ammonia emission per unit area of farmland,nitrogen runoff and greenhouse gas emission intensity of agricultural sources in Hebei Province in 2016 were significantly improved,and the average agricultural green development level of the whole province was reduced to the level of Ⅳ;the nitrogen surplus of farmland was also increased Compared with 1996,ammonia emission per unit area of livestock,nitrogen leaching of farmland and environmental cost of nitrogen per unit food of production unit decreased slightly,and environmental cost of nitrogen per unit food decreased to 91%of that in 1996.In addition to nitrogen cost,the average agricultural green development degree of other indicators is still at a low level,and the pollution of agricultural ecological environment in Hebei Province is still relatively serious.In other indicators of Hebei Province in the past 20 years,the level of social development has been continuously improved.The agricultural economic benefits increased significantly,and the agricultural output value per unit area and per capita disposable income increased by 1.96 times and 3.05 times respectively.Agricultural production capacity continued to improve,and nitrogen use efficiency increased.The utilization intensity of nitrogen,phosphorus,pesticide and agricultural film increased continuously.(2)From the perspective of spatial change,compared with 1996,the overall green development of agricultural ecological environment in Hebei Province in 2016 was at a lower level.Among the indicators of farmland nitrogen surplus and ammonia emission per unit area,the areas with higher pollution degree were mainly distributed in the south central and northeast regions,and the level IV counties in the northeast region were significantly increased compared with 1996;among the indicators of ammonia emission per unit area of animal husbandry,nitrogen leaching of farmland and nitrogen environmental cost per unit of food production,the counties with low level of agricultural green development were mostly concentrated in rivers Compared with the counties with higher pollution level in 1996,the level of green development of agricultural ecological environment in the whole province is still at a low level;in 1996,a large number of counties in Hebei Province were at level IV,mostly distributed in the south central and northeast regions,and increased significantly in 2016.Compared with 1996,the degree of agricultural green development of social development,economy and agricultural production in the northeast and south of Hebei Province showed an increasing trend.(3)The nitrogen flow in agricultural system of Hebei Province is affected by many indexes,and the influencing factors are different in different time and space,all of which have positive or negative effects on agricultural system nitrogen flow.The influencing factors of nitrogen flow in agricultural system are agricultural mechanization level,animal protein consumption ratio,food self-sufficiency rate,per capita cultivated land occupation level,agricultural output value per unit area,per capita disposable income of rural residents,heat output per unit area,plant egg white yield per unit area,nitrogen use efficiency of farmland system,nitrogen use efficiency of animal husbandry system,nitrogen utilization efficiency of food system The indexes of element use efficiency,nitrogen use intensity,manure and urine recycling utilization rate and phosphorus use intensity were determined.At present,the agricultural ecological environment in Hebei Province is deteriorating,and the risk of environmental pollution is still serious.(4)By regulating the correlation between nitrogen flow indexes in agricultural system,the agricultural ecological environment can be improved in a certain range.In the aspect of planting industry,it is necessary to reduce the amount of pesticide and chemical fertilizer,apply high efficiency,low toxicity and low pollution chemical fertilizer and pesticide,introduce advanced management mode and technology of planting industry;in the aspect of animal husbandry,we should combine agriculture with animal husbandry,control the excessive breeding of livestock and poultry,implement the whole chain management of manure and urine,and realize the harmless and resource utilization of manure and urine.To sum up,the green development level of agricultural ecological environment in Hebei Province shows a downward trend,and the development degree of other relevant indicators is gradually improved.At present,the ecological environment is still at a high pollution level,and most counties with high pollution degree are concentrated in the south central and northeast regions of Hebei Province.The ecological environment is mainly affected by nitrogen use intensity,heat yield per unit area,plant protein yield per unit area,per capita cultivated land occupation level and other indicators.The county agricultural ecological environment in Hebei Province can be improved by controlling the amount of chemical fertilizer,improving the management technology of planting industry,and strengthening the combination of agriculture and animal husbandry.