Abstract: The method of numerical simulation was used to investigate the influence of the side jet flow on the aerodynamic characteristics of gun-launched missile. Based on three-dimension N-S equations combined with S-A turbulence model, the numerical simulation of computational fluid dynamics (CFD) was implemented. It is found that the computational aerodynamic characteristics are to be in good agreement with the results from wind tunnel test. The numerical simulation for external flow field of gun-launched missile with side jet flow was performed. The result from simulating performance also shows that the side jet flow have significant influence on the flow field and the aerodynamic characteristics of gun-launched missile.