Abstract: The cumulative impacts of the cascade power stations on water temperature are studied by using the mathematic model.The water temperatue of Jinping and Ertan in reservoir area and the outflow temperature are computed.Comparison is carried out between the joint operation and single operation of Ertan.The results show Jinping reservoir is steadily thermal-stratified in the year round.The temperature at bed keeps cold steadily at 8.6℃.The temperature on the surface near dam varies from 12.7～24.2℃ in the year round.The course of the outflow temperature is obviously delayed.Ertan reservoir is thermally stratified both at the single operation and joint operation conditions.But compared with the single operation condition,the surface temperature declines and the bed temperature rises at the joint cooperation condition.The stratification in reservoir area is weakened.The delay and evenness of the outflow temperature course is further strengthened.The cumulative impact of the cascade power station on ecology environment is obvious.