The invention relates to a combined weighting evaluation method and system for power quality of a power distribution network. The method comprises the following steps: determining subjective weight and objective weight of a power quality index by adopting an improved AHP method and an improved entropy weight method respectively; and carrying out comprehensive evaluation on the subjective weight and the objective weight through a combination weighting method with maximum variance to obtain a comprehensive evaluation value result of the power quality. According to the scheme, through the combination weighting mode of objective weighting and subjective weighting, the weight obtained by the preference of the decision maker is considered, and the objectivity of decision making is ensured to a certain extent. And the evaluation values of all the obtained schemes are relatively discrete in a combined weighting manner by combining a variance maximization idea, so that a decision maker can makea relevant decision more clearly.