To scientifically and reasonably evaluate the severity of voltage sags,this paper presents a multi-level evaluation method of voltage sag based on combination of improved analytic hierarchy process and entropy weight method.This method calculates the relative importance of the duration and sag amplitude of each sag event by constructing comparison matrix,judgment matrix and quasi-optimal consistent matrix,and gives the objective weight of these two eigenvalues.From the perspective of single voltage sag event and monitoring station,this method evaluates the severity of voltage sag in different levels.The calculation results obtained by this evaluation method well correspond to actual severity of voltage sag.