In view of the inability of current fault analysis software based on COMTRADE to effectively conduct on-line automatic fault analysis and integrate with the fault information system， a set of cross-platform on-line automatic fault analysis software system based on COMTRADE is investigated and implemented using a number of cross-platform technologies. Based on the design principle of XML technology， it uses STLPORT and Macro technology to realize the cross-platform and simplest COMTRADE parse algorithm， QT4 to realize the cross-platform graphics drawing and picture generation technology， Xerces and Xalan to realize the cross-platform XML parse and transform， thereby generating the fault report in the format of HTML， WORD and PDF. It has expanded the incremental quantity detection algorithm and realized position detection for multi-fault initial data. The reliable fault phase-selection algorithm is discussed， the selection principle of single-terminal and double-terminal fault location algorithms is described. The system is successfully integrated with many fault information systems from different manufacturers， and has completed numerous automatic fault analyses after putting into operation.