In order to improve the applicability of Grid-Xin’anjiang model (Grid-XAJ)in flood simulation and forecasting of the semi-arid and semi-humid areas, the dominant runoff generation mechanism of the basin grid in the process of runoff generation was dynamically identified by determining the relationship between rainfall and soil moisture in this study. The Grid-Xin’anjiang and saturation-infiltration double excess distributed model (Grid-XAJ-SIDE)was constructed based on the dynamic combination of saturation-excess and infiltration-excess runoff. The semi-arid Suide Watershed was selected for comparing the simulation results of the Grid-XAJ-SIDE, the Grid-XAJ and the Grid-GA models. The results show that the qualified rate of runoff simulation of the three models in the Suide watershed are all above 80.0%. Compared with the Grid-XAJ (53.0%)and Grid-GA (40.0%)models, the Grid-XAJ-SIDE (66.7%)model has a higher qualified rate for the flood peak simulation. Meanwhile, the Grid-XAJ-SIDE model can capture the control effects of rainfall and soil water content on the spatio-temporal distribution of runoff generation.