Rainfall will affect the characteristics of slope flow field. Due to the continuous flow of fluid, the surface runoff and slope seepage usually exist a coupling linkage phenomenon. The surface runoff is described by the N-S equation, while the Darcy’s law is used to describe the seepage in the slope. The analytical solutions of velocity distribution, pressure and discharge as well as the semi-analytical solution of runoff surface line are derived by the separation of variables method under the velocity slipping boundary condition at the interface between runoff and soil. In addition, the explicit Runge-Kutta method is adopted to solve the water depth, velocity and discharge values at different locations. The results show that the steeper the slope is, the faster the fluid movement and the shallower the water depth is. The greater the rainfall intensity is, the deeper the overall water depth is. The flow velocity at the slope surface is not equal to 0. The closer to the downstream, the larger the proportion of runoff flow discharge is. The study can provide reference for the research of the slope flow field characteristics.