Environmental isotope ²H, ¹⁸O and ³H, temperature and electric conductivity had been used to analyze bypass abutment seepage flow of Xin'anjiang right dam. Environmental isotope data on the right dam indicate the existence of bypass seepage flow in rock. The seepage water from the drainage gallery boreholes is not only from mountain precipitation but also from reservoir water that leak bypassing the right abutment. The reason of uplift cell 3E_1-1 increasing is the result of the leakage from the fault F0. There is no seepage from reservoir to the grouted gallery through fault F1 under No. 6 and No. 7 dam section. Given the tritium is about 19.54 TU, the leakage water of G7-4 borehole comes from local precipitation of right dam. Part of reservoir water is proved to exist in the observation wells of right dam abutment. The data of environment also testified the result from the artificial tracer method.