Abstract: Based on the theory of variable fuzzy set, a method of variable fuzzy evaluation for analysis of surrounding rock stability is proposed, which can identify the relative membership degree between sample index and standard-value interval of each level index, and which can improve reliability of evaluation result in multi-index synthetic evaluation by varying model and its parameters, and which can reasonably analyze the stability of surrounding rock and determine its level.The method is demonstrated by application to diversion tunnel of the Daliushu Hydro Project, which get better results.Evaluation result of comparison of this method with fuzzy matter-element evaluation method proves that variable fuzzy evaluation method is reasonable.