Abstract: It is very important to study the influence of reservoir construction on the water temperature of the river channel and to know the changing rules of the water temperature of the reservoir, the temperature of the released water and the water temperature of the river channel. They are of great significance to the restoration of ecological environment and the biodiversity of river channel.In this paper, the laterally-averaged 2D reservoir water temperature model is used to simulate the water temperature distribution and the discharge temperature of Jiangjiakou reservoir, and the one-dimensional longitudinal temperature model is used to simulate the water temperature of downstream river waters at different years, and we focus on the research on the change of the water temperature situation in the National Aquatic germplasm resources reserve of fish at 23.6 km below the dam. The results showed that the water temperature in the reservoir is obviously stratified, resulting in the significant phenomenon of "cold-temperature stagnation" and " heated-temperature stagnation " in the river. The drop in spring and summer can be up to 3.6℃, and the increase in autumn and winter can be up to 4.1℃. By means of the one-dimensional longitudinal temperature model which is used to simulate changes in water temperature along the river with or without the influence of tributary inflow, we found that due to the water river tributary import and solar radiation influence, the water temperature along the river has effectively alleviated. The reserve 's water temperature is close to the natural water temperature, and it did not change the reserve's the original water temperature environment of fish. It will not adversely affect the normal growth and reproduction of fish in the reserve.