Abstract: In this paper, stratified sampling method was used to count and analyze the faults of CRH2 EMU Level 3 maintenance. It was compromised the occurrence rate and importance of random sample, calculated the weighted score by weighted average method to form the key fault processing database. Through the development of Key Fault aided Analyzing System based on B/S network framework, the management of classified users, added fault data, fuzzy query and other functions were implemented. It was convenient for the field operation personnel to obtain real-time processing of key fault, so as to improve the efficiency and quality of EMU maintenance.