In this dissertation, academic analysis of the influence to deflector plate in gas jet field of a Vehicle-mounted Vertically Thermal Launched missile as well as simulation study. The finite volume method, a fully structured grid, three-dimensional N-S equation is used for the numerical simulation of the process during the missile launching. The two main factors: temperature and forces on the launcher is the standard we test a launching system. The temperature on the position we test will rise with the decreasing length of the deflector. Especially, when the length is near to the potential core, the temperature changed greatly. Also, the angles of the deflector under the same length have less impacted on the temperature field. However, the force on the deflector would be change greater than the temperature with the change of angles