Aim To study the relationship between the changes of ecology and environments and the transmission of Schistosomiasis japanica after the construction of the three gorges reservoir.Methods Based on predictive data supplied by the Yangtze River Committee on Water Conservancy,of the changes of the water level and sediment in the middle and lower reaches of the Yangtze river after the dam construction, corresponding data were collected and mathematics model was extablished by field pilot studies. In order to understand the effects of changes of water level and sediment on the growth 4 distribution of Oncomelania hupensis which is the intermediate host of Schistosoma japonicum, field surveys and ecologically intimated experiments were done.The prevalence status and factors related to transmission were investigated by methods of epidemiology, geographical medicine and social medicine.Results 1 The Three Gorges Project is an integrated project in a large scale to exploit and improve the environments of the Yangtze River. It will have a profound effect on improving and accelerating China’s social and economic development. 2 Positive impact on control of Schistosomiasis after the construction of The Three Gorges Reservoir:After the dam construction, the decrease in the frequency of flooding in Yangtze River will be occurred which cease the diffusion of snails and decline the chances ofinfectionofhumanandlivestock. Snails habitats will be reduced in the flushed areas along the Yangtze River. Exploitation of beaches and delimination of snails will be benefited from the beach’s uplift in the flushed areas. And the floods that will be ahead of time in autumn will interfere the development of snails.3 Negative impact on control of Schistosomiasis after the construction of The Three Gorges Reservoir:The flushed beaches and migrator’s settlements in certain altitude may become snail habitats.The reservoir areas will become the potential transmission areas of Schistosomiasis due to diffusion of infectious resources and Oncomelania snails. The uprising of the water body level may cause the expending of the snails habitats in some place of Jianghan plain in between spring and summer.The perish of Dongting lake will be put off by the delayed flush, which causes the beach in a situation of growing reed-grass or grass for a long time that benefited to snails’ reproduction. And the chances for human and livestock being infected were increased because of the ahead of time of water regression in Dongting beach in autumn.The distribution of snails will not be affected by the changes of water level in the beaches of the downstream of Yangtze River after the dam construction, but the flushed section in Anhui in recent 80 years are suitable for the snails development.4 The environmental changes due to dam construction will not obviously affect the development of snails and the transmission of Schistosomiasis in the Poyang Lake.5 This report is an elementary study and further researches are needed.Conclusion The changes of ecology and environment after dam construction will have positive and negative impact on the transmission of Schistosomiasis in the Three Gorges area and the middle and lower reaches of the Yangtze River.We should consider the negative influences and more studies are needed in making strategies for controlling the transmission of Schistosomiasis. [ Aim To study the relationship between the changes of ecology and environments and the transmission of Schistosomiasis japanica after the construction of the three gorges reservoir. Methods Based on predictive data supplied by the Yangtze River Committee on Water Conservancy, of the changes of the water level and sediment in the middle and lower reaches of the Yangtze river after the dam construction, corresponding data were collected and mathematics model was extablished by field pilot studies. In order to understand the effects of changes of water level and sediment on the growth 4 distribution of Oncomelania hupensis which is the intermediate host of Schistosoma japonicum, field surveys and ecologically intimated trials were done. The prevalence status and factors related transmission of investigated by methods of epidemiology, geographical medicine and social medicine. Results 1 The Three Gorges Project is an integrated project in a large scale to exploit and improve the environments of the Yangtze River. It will have a profound effect on improving and accelerating China’s social and economic development. 2 Positive impact on control of Schistosomiasis after the construction of The Three Gorges Reservoir: After the dam construction, the decrease in the frequency of flooding in Yangtze River will be occurred which cease the diffusion of snails and decline the chances ofinfectionofhumanandlivestock. Snails habitats will be reduced in the flushed areas along the Yangtze River. Exploitation of beaches and delimination of snails will be benefited from the beach’s uplift in the flushed areas And the floods that will be ahead of time in autumn will interfere the development of snails.3 Negative impact on control of Schistosomiasis after the construction of The Three Gorges Reservoir: The flushed beaches and migrator’s settlements in certain altitude may become snail habitats. reservoir areas will become the potential transmission areas of schistosomiasis due to diffusion of infectious resources and Oncomelania snails. The uprising of the water body level may cause the expending of the snails habitats in some place of Jianghan plain in between spring and summer. The perish of Dongting lake will be put off by the delayed And the chances for human and livestock being infected were increased because of the ahead of time of water regression in Dongting beach in autumn.The distribution of snails will not be affected by the changes of water level in the beaches of the downstream of Yangtze River after the dam construction, but the flushed section in Anhui in recent 80 years are suitable for the snails development.4 The environmental changes due to dam construction will not obviously affect the development of snails and the transmission of Schistosomiasis in the Poyang Lake.5 This report is an elementary stud y and further researches are needed. Confluence of changes in ecology and environment after dam construction will have positive and negative impact on the transmission of Schistosomiasis in the Three Gorges area and the middle and lower reaches of the Yangtze River. We should consider the negative influences and more studies are needed in making strategies for controlling the transmission of Schistosomiasis. [