The Waisanding sandbar is a major tidal flat in Taiwan that extends about 10 km from Chiayi coastline and its sediment source is mainly from Zhuoshui River. The ebb and flow of this place produce high ecological value and form a natural breakwater to protect mainland coastline. However, the sediment source had been decreased owing to human and natural factors, causing the area of sandbar to become smaller year by year. Therefore, this area is necessary to be monitored for environmental sustainability. In this study, we utilize multiple optical remote sensing satellites in the last three decades, including Landsat/SPOT series and Sentinel-2 imageries, to track the decadal variation of the intertidal zone. We first collect historical cloud-free images since the 1990s and calculate the Modified Normalized Difference Water Index (MNDWI) to identify water pixels. After computing water appearance probability of each pixel, the map is linearly translated into actual elevation by introducing the DTU10 tide model for high tide and low tide boundaries. To validate, we use the ground truth data collected by the single-beam echo sounder and obtain and accuracy of coastal elevation model at 36 cm. In addition, we analyze different variability of Waisanding sandbar. During 1994-2017, the volume decreased from 1.88×10^7 to 1.03×10^7 m^3 and the rate of moving across the sandbar is 78.7-221.3 m yr^(-1). Among all the rates of movement, the south tip is faster than the north tip. Finally, the sandbar is projected to touch Aogu wetland around 2048.