The potential large-scale landslide site (No. T002) in Chuchi Township, Chiayi County, is primarily composed of shaly sandstone and siltstone shale strata. The dip angle of the strata is about 10~12 degrees to the north-east, which is characteristic of a dip slope. Generally, the large scale landslide and groundwater had close relationship. In the present study, to understand how rainfall in the study area affects slide conditions, we compared the soil water index (SWI) with variations in the groundwater table to correlate the displacement. The results indicated that the SWI and the variations in shallow groundwater depth were consistent. The SWI can therefore assist groundwater data when lack of monitoring data are insufficient or when the data are corrupted.