Abstract: The runoff mechanism in the hilly watersheds is usually a mixed runoff formed by the combination of multiple runoff modes. The selection of the runoff mechanism has profound significance for improving the precision of the rainfall-runoff simulation and forecasting. This article takes the Wangjiashaozhuang Watershed in Linyi City as an example. It selected 53 flood events from 1967 to 2020. It conducted a comprehensive analysis of related factors from the flow process line, rainfall-runoff relationships, climate geography and underlying surface characteristics. The mechanismis dominated by full storage runoff mode. The research results can provide a reference for the choice of hydrological models of the hilly area.