Abstract: On the Lancangjiang main stream,hydropower stations have been programming and building.The paper utilizes the Water Resource Model for the Whole Basin (WRMWB) which developed by author and colleague,and the method for analyzing hydropower station trouble to the runoff,for analysing the change process of runoff in building hydropower station.The results indicated that①The runoff process of leave country section mainly consistent to upstream water instance,but there is a slightly disturbance when low water in remote future year; ②Although upstream water instance is differ,the harassment of hydropower stations has consistency on runoff in the same scene year.Remote future year the affection is obvious most of all; ③Along with hydropower station building,harassment on runoff is more clearer within year.But annual gross runoff keep its balance;④ The model and analysis method can calculate the affection of hydropower stations harassing on runoff.It gives a way to evaluate affection of power station on hydro-environment.