To investigate the impact of land use type changes caused by urbanization on the flood process in the piedmont plain area, the Meixi River Basin and Honglai Town in its downstream plain area was selected as the research area. The land use type changes in the upstream mountainous area and downstream plain area of the Meixi River Basin from 2002 to 2018 were analyzed. Based on multi scenario numerical simulation, this study investigates the impact of land use type changes on flood processes and surface inundation in the piedmont plain area at the watershed scale. The results show that with the reduction of arable land and forest land and the increase of urban construction land in the Meixi River Basin, the runoff coefficient and peak flow in the upstream mountainous areas both increase, and the inundation situation in the downstream piedmont plain area becomes more severe. The increase of urban construction land in upstream mountainous areas has increased the peak flow of sudden floods in mountainous areas and advanced the peak time, mainly affecting the average maximum submergence depth on the surface and average peak time. The increase of urban construction land in the downstream plain area has advanced the occurrence of waterlogging, mainly affecting the average duration of surface inundation.