Abstract: Efficient processing methods are presented to improve simulation efficiency for Direct Simulation Monte Carlo(DSMC) calculation in chains of collision pair selection and time integration. Firstly, an adaptive collision distance collision pair selection method is developed with a introduced collision distance. Then, inspired by adaptive local time step technique and data structure feature of the DSMC method, an adaptive molecule time step approach is developed, in which molecule is chosen as the smallest time step adjustment unit. Finally, the feasibility and efficacy of the efficient processing methods in this paper are verified by simulating flow over a cylinder. The results show that the developed efficient processing methods can relax the cell size constraint of the DSMC method and reduce the execution computing time significantly as well as maintain the fine simulation resolution and the flow structure.