The HLA (High Level Architecture) is a blueprint to use to develop the necessary infrastructure in order to promote interoperability and reusability within the modeling and simulation community. RTI (RunTime Infrastructure), software implementation of HLA, is composed of three components: libRTI, FedExec, and RTIExec. RTI is a middleware that supports dynamic, many-to-many communication in a distributed environment. Running a large-scale distributed simulation may need a large amount of computing resources at geographically. Such environment raises serious security concerns and dynamic coordination concerns. Motivated by these concerns, we have developed the RTI that can overcome these problems using Open Grid Services Architecture (OGSA) inside Globus Toolkit3(GT3). We call it service-oriented RTI-G. In this paper, we illustrate the structure of the service-oriented RTI on Grid and how it can solve the mentioned problems.