Numerical analysis was performed based on the Material Point Method (MPM) to analyze the failure mechanisms of unsaturated slopes due to rainfall infiltration. A coupled hydro-mechanical finite element model was applied to solve the rainfall infiltration and slope instability, allowing the analysis to capture both the failure and post-failure mechanisms. Rainfall infiltrated into the surface of the slope and, when it encounters low permeability layers or impermeable layers, excess pore water pressure is formed. To examine the effect of the distribution of excess pore water pressure on the slope, the numerical analysis was conducted by varying the soil depth at the crest and toe portions of the slope. The results confirmed that pore water pressure was formed at areas with shallower soil depth. Depending on the location of the formed pore water pressure, the type of slope failure varied between progressive failure and retrogressive failure.