The influence of rainfall on the stability of vegetation slope is a hot topic in ecological slope protection. Based on MIDAS GTS/NX, and combined with the background of a slope engineering in Zhangjiakou area, common local slope protection vegetation has been selected. Slopes incloude four working conditions: Bare slopes, Festuca arundinacea vegetation slope, Buxus microphylla vegetation slope and Festuca arundinacea-Buxus microphylla mixed vegetation slope. The variation of pore water pressure with time and slope stability under rainfall condition are compared and analyzed in this article. The results show that :(1) Under the same intensity and duration of rainfall, the infiltration rates of the three vegetation slopes were lower than that of the exposed slope. Compared with the bare slope, vegetation slope has had better water-holding capacity.Among four different types of vegetation slopes, the increase of pore water pressure in Festuca arundinacea vegetation slope is the least .The soil located in the top, surface and bottom of the slope has still remained a part of matron suction.Festucaarundinacea has reduced the influence depth of rainfall. (2) After the rainfall, the Festuca arundinacea vegetation slope has had the highest safety factor compared with other vegetation slopes. Festuca arundinacea has increased the effective stress of slope soil and improved the stability of slope effectively. The above research has aimed to provide reference for the influence of rainfall on vegetation slope and guidance for vegetation slope protection technology in semi-arid areas.