Study region: The middle reaches of the Yellow River are located in the semi-humid and semi-arid regions. Study focus: The hydrometeorological and subsurface conditions of the study region possess strong spatiotemporal heterogeneity, resulting in complex and dynamic spatiotemporal variations in runoff generation mechanisms, modeling difficulties, and poor flood simulation accuracy. To precisely calculate spatiotemporal runoff-generation, we developed an initial recognition of the runoff generation mode method (Grid-based Curve Number-Topographic Index, GCN-TI) and the distributed hydrological model (TOKASIDE-D model) with spatiotemporal dynamic saturation-excess and infiltration-excess runoff generation modes (SE-IE modes) for SE-IE runoff modes process reproduction and the spatiotemporal analysis in three selected watersheds. New hydrological insights for the region: The proportions of infiltration-excess grids identified using the GCN-TI method are within 5 %, 10-20 %, and above 70 %, respectively. The TOKASIDE-D model improves the flood simulation accuracy by 10-30 %, and the error ranges of each evaluation indicator are further reduced. For each watershed, there are three types of spatiotemporal dynamic changes for SE-IE modes. The "descending type" mainly applies to the semi-humid Chenhe Watershed, the "undulating type" to the Dongwan Watershed with short-duration heavy rain, and the "ascending type" applies to the semi-arid Suide Watershed. The proportion of the SE-IE modes conversion for the runoff generation modes within the entire flood duration does not exceed 50 %, mainly occurring during the main rainfall period. The SE-IE modes conversion time is significantly affected by soil water content.