The rainfall patterns in Taiwan changed in recent years due to the impact of global warming and climate change. In this study, groundwater variation at colluvium slope located in Taiwan Highway No. 18 and alternating sandstone and shale slope located at Taiwan Highway No. 20 were investigated. Besides collecting the local precipitation and geology information, borehole drilling and electrical resistivity tomography test were performed to clarify the depth and the distribution of the underground geologic formations. In addition, monitoring devices, such as inclinometers and ground water level meters, were installed to monitor the slope and ground water level. Finally, the finite element analysis was conducted to integrate the results from observed geology soil layer structure, permeability of bedrock, slope sliding direction, and depth of sliding to the result of limit equilibrium method.