Abstract: This paper takes the hidden dangerous Karahayisu Landslide in Xinyuan County, Xinjiang as a research case, and uses the COMSOL Multiphysics numerical simulation finite element software to establish a calculation model for landslide stability based on unsaturated seepage theory and Mohr-Coulomb criterion. The numerical simulation results give the original stress distribution and initial pore pressure distribution of the landslide in the study area, the internal stress, effective plastic strain, plastic zone, water content and potential slip surface distribution under rainfall infiltration conditions. The safety factor of the slope under rainfall infiltration is calculated. Based on the model calculation, the safety factor of the sliding slope decreases with the increase of rainfall under different infiltration conditions. The critical rainfall threshold of the sliding slope can be gained based on the variation of the safety factor. This study proposes a different way to calculate the rainfall threshold of rainfall-induced loess landslide using the strength reduction safety factor, also provides an effective method for studying the critical rainfall threshold of rainfall-induced loess landslide.