In view of the problem of information redundancy between traditional quality evaluation indicators of underground rock mass,8 indicators,such as the uniaxial saturated compressive strength of rocks,the RQD value of quality indicators of rock mass,and the status of structural planes,are selected as evaluation indicators for an undersea metal mine in China.The first 2 principal components with a variance cumulative contribution rate of 94.873 % are obtained by dimensionality reduction of the evaluation indexes using principal component analysis (PCA),and 5 rock mass quality grades are constructed based on the single index classification interval to build an EWM-TOPSIS evaluation model for rock mass quality evaluation.The results of the study show that the PCA-EWM-TOPSIS coupled method achieves 88.2 % accuracy for the quality grading results of rock mass with respect to the traditional topological assessment method,and the evaluation results basically agree with the evaluation results of the topological assessment method,and the PCA-EWM-TOPSIS coupled method solves the problem of the over-redundancy of the evaluation indexes,greatly simplifying the calculation process and improves the efficiency of the quality evaluation of rock mass.The method has good engineering application potentials and can be applied to underground rock mass quality grading.