Abstract: The paper presents an improved DSMC(Direct Simulation of Monte Carlo)-IP method that has been combined with unstructured grid and IP(Information Preservation) method, and uses the method to simulate a three dimensional hypersonic rarefied flow field. The gradient scale unstructured grid is used to meet the DSMC computational requirement and describing the characteristics of the flow field; the flux computational format in IP method is improved using the Van Leer format to solve the numerical discontinuity problem in the shock region; the cell information preservation method is proposed to improve the stability of the IP method. The feasibility and effectiveness of the improved DSMC-IP method is validated by the simulation results of flow across a sphere and the head of a space vehicle, and the aerodynamic characteristics and regularity of parameter distribution are analyzed.