Abstract: To investigate the establishment process of opposing jet and its transient influence on the spiked blunt body in hypersonic flows, an in-house code which employs high-resolution numerical schemes was developed to solve the unsteady Reynolds-averaged Navier-Stokes equations. At first, classical experiments were applied to validate the code in simulating complex flow field including shock interactions. Then, the establishment process of opposing jet was thoroughly investigated. The obtained results show that establishment process of opposing jet and complex shock wave evolutions are clearly presented. The flow features change dramatically during the whole process. Besides, the pressure and heat flux along the blunt body change rapidly and the aerodynamic drag firstly drops to a minimum value and then increases to a relatively larger stable value. Furthermore, increasing the total pressure ratio of opposing jet would lead to more severe fluctuation in aerodynamic drag after it drops.