A distributed Green-Ampt rainfall-runoff model based on orthogonal grids was built and applied to two semi-arid basins in the Loess Plateau of Northern Shaanxi Province to test its performance. The results show that in the two semi-arid basins, the distributed Green-Ampt model performs better than the GA-PIC model and the traditional Green-Ampt model, especially in the flood peak simulating. The distributed Green-Ampt model has higher accuracy in simulating the time from the confluence to outlet section of basin with the grid-based slope confluence and river confluence module. In addition, the distributed Green-Ampt model is able to calculate the runoff process at different locations of the basin more accurately, and also able to simulate the runoff area distribution of the basin more accurately. The spatial and temporal distribution of rainfall in the semi-arid area is uneven and the infiltrated-excess runoff is mainly affected by the rainfall intensity,therefore the rainfall observation accuracy has a great impact on the runoff forecasting accuracy.