Abstract: The construction of reservoirs has a certain impact on the environment while bringing great economic benefits to flood control, power generation, irrigation and water supply. In particular, the water temperature of the downstream river is changed by the discharge of reservoirs, which disturbs the natural rhythm of swimming, plant reproduction and growth, while the cascade reservoir undoubtedly magnified this effect. In order to study the limited effect of reservoir cascade construction on water temperature, the virtual reservoir Alpha was constructed, and the Alpha reservoir was connected infinitely with the first and last ends, and then the water temperature of the cascade reservoir was simulated by the two-dimensional mathematical model CE-QUAL-W2 with the average width. The results show that the cumulative impact of water temperature brought by the cascade development of river is limited, and the cascade temperature has greatly weakened the water temperature stratification phenomenon, but the hierarchical structure of the reservoir will not disappear; after the adjustment of 22 cascades, the discharge temperature of the reservoir does not change relative to the temperature of incoming water, both the water temperature on the surface and bottom of the reservoir are the same as those of the upstream cascade, and the flow field of the reservoir area is also the same as the upstream flow field; when the cumulative impact of water temperature in the reservoir reaches the limit, it indicates that the heat of the inflow and outflow reaches the equilibrium completely.