Abstract: Considering the inconsistency among the evaluation results drawn by different classification methods for surrounding rock quality of tunnels, combination evaluation idea is introduced . A model for classification of surrounding rock quality based on combination evaluation is formulated by selecting several existing classification methods for surrounding rock quality of tunnels as the fundamental methods, which may integrate the advantages of the fundamental methods. Since the physical meanings and dimensions of the evaluation indexes drawn by the fundamental methods are different, a standardized method for evaluation indexes is developed to make the evaluation results of different fundamental methods comparable so as to solve the computational problem of the calculation model based on the combination evaluation. Taking into account the differences of rationality between the evaluation results of the fundamental methods, a method for reasonable degrees of the fundamental methods is established by introducing drifting degree, based on which the weight calculation is developed. Then the combination evaluation method for classification of surrounding rock quality of tunnels is developed to make the classification method of surrounding rock quality of tunnels more reasonable, which can not only solve the problem of inconsistency among the fundamental methods, but also give full play of the fundament methods’ advantages and avoid the un-reasonability. Finally, the proposed method is used to analyze practical projects. It is shown that the proposed method is feasible and reasonable.