In CFD-DEM coupling calculations, an excessively large selection for particle calculation time step affects the calculation accuracy, and an extremely small selection affects the calculation efficiency. A search ball is constructed by taking each target particle as the center particle with the fastest displacement in the calculation domain. Subsequently, the particles that may collide are screened to establish a search list, and a forward search method is used to determine particle collisions. Finally, a particle calculation time step is proposed. The improved DEM method, which automatically adjusts the collision time, resolves the contradiction between particle calculation time step selection, accuracy, and efficiency. The relative error between the numerical simulation results of particle collision and the theoretical solution was less than 3%. The three calculation time steps selected in this study can guarantee excellent calculation accuracy and efficiency. For multi-particle and fluid coupling simulations, the traditional CFD-DEM method selects 10-7s or less in the calculation time step to obtain an accurate solution. The method proposed in this paper selects 10-5s to obtain an accurate solution, which increased the calculation efficiency by 19.8%.