Abstract: Rainfall and earthquake, both of which are of great uncertainty, are two of the most principal factors for landslides. Seismic activity is frequent in Xiakou area, Ya'an, Sichuan, although this area is located in the VII zone of seismic intensity. Furthermore, rainfall and groundwater table in Xiakou area sharply vary with seasons. Triggered effect on landslides is consequently strong and stochastic. Studies on the randomness of triggered foctors are crucial for the slope reliability. The method for the slope reliability anlysis based on Monte-Carlo method and residual thrust method is improved statically to take the randomness of groundwater and seismic force into account. Considering the randomness of mechanical parameters of slope, seismic forces and pressures of groundwater, the reliability analysis on Xiakou slope is conducted to quantify the contribution of triggered factors to the reliability of Xiakou slope. Analytical results show that randomness of groundwater table has a strong effect on the slope reliability. On the contrary, effect of randomness of earthquakes on the slope reliability is weak. However, seismic forces have a great influence on the stability factor of slopes.