To improve the maintainability, scalability, and reusability of models in complicated Missile Weapon System simulation, the system of a hardware-in-the-loop (HIL) simulation system based on high Level Architecture (HLA) and Modelica is designed, which can satisfy the need of interoperability among federates, and the simulation model library of missile based on Modelica is developed. Simulation application of missile trajectory and scene simulation is devised and is introduced into the federation to achieve the interaction between them and other federates. New simulation application incorporated with latest simulation technology can easily be introduced into the existing simulation system if they are in accordance with the HLA standards. The scene simulation application provides developers with a visual method to assess the performance of the system, which works as a federation in the HLA-based system. The results of missile trajectory simulation and scene simulation are given. The reusability of Modelica-based missile model provides designers with great flexibility and reusability in developing new missile models.