In this study we implement the InSAR technique for identifying the seasonal surface deformation in the SW Taiwan. The focus of our investigation is on the Pingtung plain, a tectonic valley with a high water-pumping rate. Our preliminary results show that the land subsidence occurs specifically in the dry season and even ceases during the wet season. Whereas local land subsidence is usually caused by dewatering of sediments, we compare therefore our InSAR observations with the groundwater data of this area. This comparison shows that the subsidence rate is associated with the descending trend of groundwater level. Based on our research results, we infer that the dewatering during the dry season removes the buoyant support from the sediments and the effect of sediment compaction simultaneously results in local land subsidence. This successful test exhibits that with suitable images, the InSAR is a useful high-resolution tool for monitoring the earth surface deformation and can provide significant information for the issue of natural hazard mitigation.