Abstract：First，the main factors for the classification of rock quality are selected by carefully analyzing all the influencing factors of rock quality in underground structures. Then，on the basic of analyzing the relationship of the influencing factors and fuzzification of rock quality，the model of two-stage fuzzy synthetic judgment is established to classify the rock quality by using fuzzy mathematics theory. After solving the problems of determining degrees of membership，basic weight value，and erecting their algorithm，a method of two-stage fuzzy synthetic judgment is developed. Finally，by using the idea of changing weight value，the theory and method of two-stage fuzzy synthetic judgment with changing weight value on the classification for rock quality is brought out，which can reduce the influence of subjectivity of judgment on the classification of rock quality and make it more reasonable. Compared with other classification methods，it shows that the proposed classification method is both practicable and reasonable.
