Data display that Chi-Chi earthquake affects the subsurface hydrological system in the Choushuishi alluvial fan, but relations between the changes of the hydrological system and earthquake need to be clearified. According to the groundwater level data of the groundwater monitoring well network in the Choushuishi alluvial fan, we make use of the concept of fractal dimension to analyze the possible correlation between the changes of water level and the factors of earthquake. The results show that the fractal dimension of water level changes is close to that of earthquake intensity and vertical displacement while the fractal dimension of the peak ground acceleration is smaller. We conclude that earthquake intensity and vertical displacement are the important factors that influence the changes of water level.