To meet the requirements in developing distributed simulation technology, a grid-based distributed simulation platform (GDSP), which was based on latest grid technology and high level architecture (HLA), was proposed. GDSP is the base infrastructure of service-oriented simulation support environment. And it can run simulations on wide area network efficiently, realize share and reuse of simulation resources, and improve load balancing capability of the system. GDSP introduces an information assurance challenge and details of a simulation must be guarded from unauthorized access. However, HLA doesnpsilat provide any security mechanism. So a security policy and a corresponding security architecture for GDSP were developed and discussed in detail. The security architecture uses proxy and multiple certifications mechanisms to provide an authentication and access control infrastructure that allows simulations based on GDSP to operate securely in heterogeneous environments. At last, the performance impact of the security architecture on GDSP was tested and the result showed the impact was little.