In the hardware-in-the-loop simulation environment of a certain type of tactical missile, the real-time simulation software which is developed based on the Windows XP platform is needed for simulation calculation and simulated launch control. By analyzing the overall architecture of the simulation system and the real-time principle of RTX, as well as studying the characteristics of real-time VMIC in RTX environment, the real-time communication process of software is designed, and the simulation software of the transmission control unit, based on Windows XP+RTX environment, is developed. This design enables software control of simulated launch of missiles and real-time communication of data. According to the results of hardware-in-the-loop simulation experiments, the simulation software meets the requirements.