In order to scientifically understand the effect of the construction of check dam system on the erosion dynamic process in small watershed on the Loess Plateau, the storm flood process in the Wangmaogou small watershed was simulated by coupling the distributed hydrological model MIKE SHE with the one-dimensional hydrodynamic model MIKE 11, and the erosion dynamic parameters of the different sections of the main ditch as well as the sediment reduction benefits of different combination of dam types were calculated. The results showed that:(1) The erosion dynamic distribution of the gullies in the small watershed was changed by dam construction, and the erosion dynamic parameters of gullies decreased the most after the dam system was completed. (2) The runoff erosion power varied greatly in the upper and middle reaches, while tended to be stable in the lower reaches, and the runoff erosion power in the lower reaches was obviously lower than that in the upper reaches. (3) The construction of check dam could effectively reduce the sediment transport in the watershed. When the key, medium and small dams were built separately, the sediment transport modules were reduced by 24.74%, 47.11% and 64.11%, respectively, compared with those without dams in the watershed. After the completion of the dam system, the benefit of sediment reduction was the most obvious, and the sediment transport modulus was reduced by 83.92%. The research results were intended to provide scientific reference for evaluating sand reduction benefits of check dam on the Loess Plateau.