This study applied satellite SAR images from ERS-1 and ERS-2 for water line extraction and change detection along the west costal area, covering from Kuan-in, Taoyuan to Tung-Kang, Pintung a total of about 400 km long. The images were acquired in the years of 1996 and 2005 with 10 years time span with 23 image tracks (total 92 image sets of 100 km by 100 km) In particular, the environmental sensitive areas of Fang-Yuan, Hai-Feng-Dao Chou, and Wai-San-Ting Chou, were chosen for detailed analysis. In addition to SAR images, we also incorporated optical satellite images, water depth map from Water Resource Bureau, and tidal records from tidal stations operated by Central Weather Bureau. This is important to ensure all the water line can be calibrated to the same tidal level. From the results, it is found that Wai-San-Ting Chou moved southward about 700 meters during 10 years period and it was shrunk to just one-third of its size in 1996. It is also found that the surroundings costal waters of Wai-San-Ting Chou and estuary of Pei-Kang River moved inward to west costal. The water channel was becoming more deposited as a result. Finally, Hai-Feng-Dao Chou itself moved southward about 1.5 km although its size remained quite the same during 1996 and 2005, and it also presented a clear tendency of inward moving. From the results we reported here, it is concluded that satellite remote sensing by SAR, aided by ground tidal data, bathematric map, and optical images, provides an effective and efficient tool for costal water changes in terms of large area coverage and long time span.