Abstract: To accurately and comprehensively reflect the reality of power quality in the power system, a method for comprehensive evaluation of power quality based on grade correlation degree is proposed. Firstly, establish evaluation system of power quality indexes based on index ratings divided by national standards. Secondly, subjective weights aggregating evaluation opinions of multiple experts are established by rough analytic hierarchy process(AHP). And objective weights are calculated by criteria importance through intercriteria correlation(CRITIC) according to standard data. Subjective weights are combined with objective ones to determine comprehensive weights. Then, construct a normalized matter-element extension model. Power quality grades of objects and indexes are determined through their grade correlation degrees. Power quality is evaluated and ranked according to the evaluation values of grade determined by correlation degree, which leads to a comprehensive evaluation of power quality. Finally, through case study, the accuracy and effectiveness of the proposed method is verified and it is able to provide criteria for improving the power quality.