The sentinel-1 Synthetic Aperture Radar image analysis technology is conducted to measure river width in a multitemporal change in this study. With the field surveying work, two Sentinel-1A images taken on March 14 and May 24, 2018, have been obtained. Next the SNAP data processing software can be used to produce backscattering coefficient, and the values can be converted into intensity image. Low intensity features related with water body will be helpful for river width measurement. Moreover, an UAS flight also arranged on May 24 to take 525 photos with a DJI Phantom 4 Pro UAS under flying altitude of 120 meters. The Agisoft Photoscan Professional software used to produce an ortho-mosaic image in a spatial resolution of 3.39 cm for the comparison of geometrical differences in river width measurement. According to the comparison results with manual measurement, the derived difference of river width is 1.2 meters at the Zhongtou bridge in the Wuxi river.