Studying on related work about HLA extension, two typical problems of HLA distributed simulation interoperability and reusability are focused on, and a decoupled architecture of HLA extension is proposed based on web services. A prototype is implemented based on pRTI and AXIS SOAP engine. Encapsulation and deployment of RTI services, as well as a remapping of the RTI API calls to SOAP is demonstrated by exemplars. The extension can encapsulate intrinsic RTI library and extend traditional HLA distributed simulation application to WAN ; has strong compatibility ; can be used to accomplish loose coupled and cross-platform distributed simulation system.