SOAP is a new generation distributed computing protocol on Internet. After analyzing traditional distributed objects based mobile agent systems, this paper introduces the approach to developing mobile agent systems based on the SOAP protocol, proposes the architecture of the mobile agent system based on SOAP, and presents the implementation techniques based on.NET platform, including the migration mechanism, the communication mechanism based on SOAP, the message presentation based on XML, the interoperation support of Web services, etc. Such a system has better flexibility and expansibility, and is suitable for loosely coupled Web-based computing environments.