Abstract: Gas model can have significant influence on the efficiency and accuracy of hypersonic vehicle’s reaction control system (RCS) hot jet interaction flow field simulation, the choice of gas model in numerical simulation is an important issue remains to be solved. Based on reaction jet hot gas’s physical and chemical reaction model and by solving three dimensional Navier-Stokes equation with chemical reaction source term, numerical simulation method of hypersonic vehicle’s reaction control system hot jet interaction flow field is established, by using chemical reacting flow, chemical frozen flow, binary gas model and simplified air jet model, numerical simulation of typical configuration’s hot jet interaction flow field is carried out, based on the simulation results, the influence of different gas model on hot jet interaction flow field structure and hypersonic vehicle’s aerodynamic characteristics is studied, the influences under various flight altitude and flight speeds are also discussed in detail. The result shows that: among the above four different gas models, chemical reacting flow model has higher precision, its result agrees better with wind tunnel experiment data than other three simplified models. In this paper’s low flight altitude conditions, using simplified model for hot jet interaction flow field simulation will underestimate the boundary layer separation length, which will introduce error to the prediction of vehicle’s aerodynamic characteristics, it will also underestimate the surface heat flux near nozzle exit, which is unfavorable for the design of thermal protection system. As the flight Mach number increases, the error introduced by simplified models increases, while the discrepancy between different simplified models also increases. In this paper’s high flight altitude conditions, the discrepancy between different gas models decrease, for these cases, simplified models are good to use for their high computation efficiency. These results can provide reference for future numerical simulation of hypersonic vehicle’s hot jet interaction flow field and the design of hypersonic vehicle’s reaction control system.