This paper is concerned with a power quality evaluation method based on the improved entropy method，which fixes the problem of the traditional entropy weight method that entropy weights present a wrong message of entropy when all the entropy values are close to1.The proposed method achieves efficient performance by designing a back propagation（BP）network calculation model.Firstly，the synthetic weights of power quality indices are calculated by sequential correlation analysis and the improved entropy method，thereby by passing the one-sidedness of being subjective or objective.And the quantitative values of multi-index are obtained.Then a BP network calculation model is designed to make the evaluation method more efficient and more practical.The evaluation by a power supply bureau has verified the effectiveness of the proposed algorithm.