Due to several reasons, there is a shortage of water resources in Taiwan, despite abundant rainfall. These reasons include high population density, uneven spatial and temporal distribution of rainfall, and rivers with steep gradients. According to the data collected by Central Geological Survey in the project: Pumping of Groundwater Resources in the Central Division of Mountain Areas of Taiwan, the abundant underground water in mountain areas exists in areas with thick regolith, broken rock or sandstone. Therefore, the investigation of regolith depth distribution would help us to further understand the amount of underground water, and the areas that can be exploited. This study is based on 441 drilling data over the Da-Chia and Choshui river basins, and aims to construct a relation model of topographic and environmental variables and to estimate the regolith depth in the study area. The amount of drilling data will be increased each year so that the model can be improved, developed and converged. Moreover, it can help in developing a model that is most suitable for estimating regolith depth in Taiwan.