To quantify the influence of root water absorption on unsaturated soils slope stability and provide reference for plant species selection of vegetation slope protection, a two-dimensional slope was established by COMSOL Multiphysics. The distribution of pore-water pressure in unsaturated soils slope caused by root water absorption under different root morphology, root length and rainfall conditions was simulated, and the slope stability factor was quantitatively calculated using the limit equilibrium method. Results demonstrated that the suction generated by the exponential root uptake water is the largest, which is 4.2 times larger than that of the bare slope, and the suction generated by the parabolic root uptake water is the smallest, which is still 2.7 times larger than that of the bare slope. The longer the root was, the greater the influential depth of water uptake was. The shorter the root was, the greater the suction generated, and the more remarkable the change of suction on the slope surface. After short-term rainfall, the suction of root soil slope was still 12~20 kPa higher than that of bare slope. The exponential root system contributed more to the stability improvement of unsaturated soils slope, which was 1.54 times higher than that of bare slope. While the parabolic root system was the smallest, but it was still 1.36 times higher than that of bare slope. The root water absorption has a positive effect on the stability of the unsaturated soils slope. For vegetation slope protection, priority will be give to the vegetation with the exponential root.