Quantitative GSI system and Hoek-Brown strength failure criterion can reflect the geological environment of rock mass,so they are often used to estimate mechanical parameters of rock masses. Previous determination of GSI is lack of considerations for spatial relationships between unloading cracks and slope. Correction method to the slope failure mode and structural plane in CSMR system is adopted to determine mechanical parameters of unloading rock mass in the dam abutment slope of hydroelectric power statlan in Southwest China.