The classitication of rock mass stability has close relation with selecting min-ing method and support pattern,In this paper the fuzzy synthetic judgement method is uesdfor classfying rock nass stability.On the basis of the principle of fuzzy transformation ahdmaximum subordination degrec as well as condidering all the factors in relation to rock massproperties the methOd carried out comprehensive judgement on the rock mass stabilitv, Themethod described in the paper has advantages as follows :the mathematical model it simple,application is easy and the judgement on muItiple factor complex problem may gain batter re-sult.