单位线法是现行洪水计算和洪水预报中常用的一种方法。纳希瞬时单位线具有一个较严密的数学函数式,模式中的参数(n×K)是一个揭示流域汇流本质的参数,物理概念明确,便于综合分析。纳希单位线是一种概念性的模式,由于模式未考虑流域非线性因素,有时使计算成果发生偏差。在实践中这种概念性模式不断得到发展和完善。近年来,水利水电科学研究院和南京水文研究所在纳希瞬时单位线模式基础上,提出了一种由实测资料推求一次洪水中不同时段净雨强度条件下相应不同单位 The unit line method is commonly used in current flood calculation and flood forecasting. The NACHI instantaneous unit line has a more rigorous mathematical function. The parameter (n × K) in the model is a parameter that reveals the nature of the catchment. The physical concept is clear and it is convenient for comprehensive analysis. The Nash unit line is a conceptual model. As the model does not take account of the non-linearities of the river basin, it sometimes makes the calculation result deviate. In practice, this conceptual model has been continuously developed and improved. In recent years, based on the Nathan instantaneous unit-line model, Institute of Water Resources and Hydropower Research and Nanjing Institute of Hydrology, this paper proposes a method to deduce, from observed data, the corresponding units under different conditions of net rainfall intensity in a flood