Aiming at the demand of evaluating voltage sag severity considering both electric utilities and users,an evaluation method based on power system and equipment sensitivity analysis is proposed. Initially,based on the focus of voltage sag assessment on system and user-side,the comprehensive attribute set is formed. The system-side index set is constructed with the average influence degree index as well as the voltage sag frequency index,further forms a comprehensive evaluation index set with the failure rate index. The average influence degree index is formed based on cumulative distribution density functions,statistical table and severity indices. The failure rate index is formed based on the comprehensive voltage tolerance curve and energy loss calculation. Then,the indices are weighted and Mahalanobis distance-based technique for order preference by similarity to ideal solution (TOPSIS) is used to reflect the voltage sag severity levels. The simulation model of the IEEE 30-bus system is built so that the proposed method could be used to evaluate the voltage sag severity. The result could help find out the nodes which suffer from greater impacts of voltage sag events. Finally,the fuzzy C-clustering method is used to analyze the evaluation results. It is verified that the proposed evaluation method is helpful to overcome the one-sided problem of single index evaluation.