HLA can facilitate the interoperability and reuse of all types of simulation systems; however, several drawbacks have affected its wide application in commercial communities, such as binding of interface specification to programming languages, and insufficient integration with commercial technologies. Web service has some attractive features on platform/vendor independence, and hence Web service enabling of HLA-based distributed simulation is promising for adding value to HLA. Based on the analysis of HLA's drawbacks and Web service's advantages, Web service enabling of HLA is introduced, interoperability on those two contexts is compared, and three levels of realizing Web service enabling of HLA are analyzed. Then, related research is surveyed, and key issues and their solutions to realizing a Web enabled RTI are discussed; Finally a prototype is designed, and experiments show that it can primarily implement Web service enabling of RTI.