The objective of this research is to study the impacts of slope disasters in mountain areas in central Taiwan under hydrogeology and extreme weather conditions. The failed slopes in these areas were identified, synthesized and investigated. The study synthesizes the parameters required for the future numerical modeling including soil water characteristics curves of colluvium soils, classified as GP, in central Taiwan. Samples are taken from the in-situ site which failed during Typhoon Morakot. The numerical program, FLAC, is used to back calculate the possible shear strength of the colluvium formation during failure and to obtain the possible failure shape. The results show that the location and angle of rock strata will influence the shape and depth of landslide.