Abstract: Considering the inconsistency among the references to calculate the drifting degree according to different classification methods for surrounding rock quality of tunnels based on drifting degree and the incomparability of their calculated results, the concept of support degree is introduced to calculate the weights of the fundamental methods. A new mathematical definition for the support degree is established by considering two aspects of similarity and difference degree, while the existing formula for support degree just considers the latter. The synthesis support degree of holistic data to the evaluation results of each fundamental method is calculated and used as the weight of each fundamental method to calculate the comprehensive evaluation results. Thus, a new combination evaluation method for the classification of surrounding rock quality of tunnels is derived. It avoids the inconsistency among the evaluation results by different classification methods, and the references for drifting degree so as to make the weights more realistic and make the theoretical basis firmer. Finally, the proposed combination evaluation method is applied to practical projects. The rationality and feasibility of the new method is verified.