Abstract: In order to study the influence of different time steps and runoff generation and confluence calculation methods on flood simulation in semi-humid and semi-arid regions, we simulated 12 representational flood events in Beizhangdian Basin from 1993 to 2005. The HEC-HMS model was applied to simulate the hydrological process under different time steps (10,15,20 min) and two schemes. The first scheme was the initial-loss and stable seepage method＆Clark unit line method, the second one was the Green and Ampt method＆SCS unit line method, and both schemes used the Muskingum method for river channel routing and the exponential regression method for base flow calculation. The results show that the time step has a great influence on the simulation results and both schemes had the highest simulation accuracy under 15min time step, indicating that the shorting time step does not always lead to accuracy improvement. When the time step was 15min, the average deterministic coefficient of the first scheme was 0.813, and the second scheme was 0.764. The first scheme is superior to the second one in terms of flood peak, flood volume and flood peak time.