Objective This study aims to investigate the morphological change process of scour holes at the headcut of ephemeral gullies on slopes with typical herbaceous communities and their main controlling factors. Methods Field runoff scouring experiments were conducted on slopes covered by three typical herbaceous communities in the loess hilly-gully region （Stipa bungeana， Lespedeza davurica， and Artemisia gmelinii）. Close-range photogrammetry was applied to monitor morphological change processes of scour holes. Results 1） Significant differences in root mass density and soil properties were observed among different herbaceous communities. In the topsoil layer （0~0.2 m）， the Artemisia gmelinii community exhibited significantly higher root mass density， root length density， total porosity， saturated water content， and aggregate mean weight diameter than the other two communities， while soil bulk density， cohesion， and penetration resistance showed the opposite pattern. 2） Herbaceous communities significantly affected the morphological characteristics of scour holes and their change processes. Morphological parameters， including width， height， depth， area， volume， shape factor， and depth-to-diameter ratio， showed fluctuating variations with scouring duration， following an increase-decrease-increase trend. Significant differences in morphological development of headcut scour holes at gullies were observed among different herbaceous communities， with the slowest development in the Artemisia gmelinii community， followed by Lespedeza davurica and Stipa bungeana. 3） Pearson correlation and partial least squares （PLS） analyses showed that root mass density， root length density， total porosity， saturated water content， and aggregate mean weight diameter significantly affected scour hole depth. PLS structural equation modeling （PLS-SEM） indicated that vegetation root traits and aggregate mean weight diameter were key factors affecting scour hole depth development， with total effects of -0.65 and -0.53， respectively. Vegetation roots significantly increased soil aggregate stability， thereby inhibiting scour hole development. Conclusion The findings provide important theoretical support for understanding mechanisms by which vegetation restoration influences headward erosion in ephemeral gullies.