The paper explains the role of precipitation, infiltration, subsurface water and surface water in the small forested watershed. The authors consider the infiltration and the rapid flow in soil were very important in stormflow generation processes, in, which the subsurface water contributed more than surface water did.Generally speaking, the infiltration rate and the capacity of water storage in forested watershed are very large, which implied the Horton's theory or other current models of stormflow' generation do not work there,In the contribution area, the saturated state was resulted from the rising of groundwater or the development of saturated zone above the groundwan ter.Therefore, the generation and maintenance of the contribution area depended on the infiltration and lateral flow and the surface water could be considered as the "return flow".The quick response of the subsurface water discharge to the rainfall is considered to be caused by the break of an equilibrium of forces acting on air and water in the capillary fringe, that is, by the quick conversion of the tension-saturated capillary fringe into the pressure-saturated zone. The equilibrium of forces acting on water in the capillary fringe can be broken either by the increase of the pneumatic pressure of the entrapped air with successive rainfall or by the rainfall directly when the capillary fringe just near to the groundwater surface.