Based on rock mass characteristics of Maerdang hydropower station,the quantification index of unload zoning was presented and the loosen rock is divided into several different groups according to macro-geology characteristics of loosen rock mass,frequency of joints,the ratio of longitudinal wave velocity of weathered rock mass to that of fresh rock mass and coefficient of permeability,etc,al.In the end,the paper summarized the regular pattern of rock mass unloading systematically and that enriched the theor...