Abstract: Check-dams have a significant effect on water and soil conservation, but there are great difficulties in the scientific assessment of water and soil conservation benefits of the check-dams. On the one hand, check-dams' physical mechanisms are still not clear, and their observations are limited and difficult to obtain. In this paper, the check-dam module of DYRIM has been improved and verified based on the conceptualization of the drainage mechanisms of pipes and spillways and the overall operating mechanisms, then the runoff and sediment discharge were simulated and the water and soil conservation benefits were assessed based on the improved model. The results showed that:without the check-dams, DYRIM had good feasibility during the approximate natural state (from 1979 to 1986) when there were fewer check-dams, while it had poor feasibility during the disrupted state (from 2007 to 2012) when there were more check-dams with the simulated runoff and sediment discharge were much higher than the observation. With the mechanism of check-dams were considered, the modeling accuracy was improved a lot during the disrupted state except for some year, the range of daily runoff NSEs were increased from -51.085~0.450 to 0.134~0.802, the range of daily sediment discharge were increased from -56.740~0.390 to 0.066~0.857. The impact of check-dams was evaluated with the improved DYRIM, the interception effect of check-dams contributed to decreasing the runoff volume and sediment load by approximately 14.2 million m³ and 5 million tons annually, which accounted for 40.9% and 50.3% of the total runoff and sediment respectively. The results look forward to providing theoretical support for understanding the regulating mechanisms of check-dams on the dynamic process of water and sediment and scientific guidance for the check-dam construction plan.