According to the features of complexity and uncertainty of post assessment for hydropower project environment,combining with the actual situation of Shenxigou hydropower station of Dadu River basin and identiying environmental impact assessment factors,the paper established the index system of environmental impact post assessment for Shenxigou hydropower project. Then,it comprehensively analyzed the operation of Shenxigou hydropower station through AHP and fuzzy evaluation. The result shows that AHP combining fuzzy evaluation possesses applicability,and the impact of operation of Shenxigou hydropower project on environment and social economy is in the second stage (minor adverse impact), and is biased in favor of the third level (no impact).