The measurement method is limited during the hot-test of rocket engine, in order to details each parameter distribution of internal flow field and guide the design of thin film cooling system, both single-step global reaction model and 9 components 14 chemical reaction model are used for three-dimensional numerical simulation which is on the basis of the hot-test. The numerical simulation results of two chemical reaction models are compared and show that the pressure results of the internal flow field are almost the same and accord with the experiment pressure value. However, there is a big difference between the two numerical simulation results in temperature and components distribution. The temperature of single-step global reaction model is higher. The necessity of N_2 thin film cooling system is verified by high temperature area between convergent section and throat, and the design of N_2 thin film cooling system could be directed by the numerical simulation results.