At present, XML-based distributed application system is the application of WEB technology in the new distributed file processing system. The framework of distributed application system is discussed, XML-based transmission protocols, such as simple object access protocol, and the system framework of distributed application system composed by combining XML and component technology is given. Then, an XML-based distributed application system was designed, and the basic components were customized in the system: MYHTTP.DLL, MYSOAP.DLL, mytest.dll, which are used for basic HTTP, SOAP operations and transaction processing. Finally, the communication mechanism between components is explained.