To solve the parsing problems due to the difference among COMTRADE standards， unreadable code in remote transmission and incompleteness of data in the power system， this paper presents an algorithm that can correctly parse the file in the COMTRADE format to the greatest extent. The algorithm includes the error pre-analysis part and the fault-tolerance parsing part. With the method of line-skipping parsing and validation， the error pre-analysis part can find all sorts of error that can influence the proper parsing and ultimately form an error information table. By inquiring the error information table and COMTRADE extension character table to parse the data file and obtain the validation information in advance， the fault-tolerance parsing part will reliably realize fault-tolerance parsing of file in the COMTRADE format. Plentiful testing results of field data show that the new algorithm is practical and reliable， which can provide technical references to the development of any third-party transient data analysis software in a power system.