Abstract: As the dynamic reserve land resource, tidal flats contain significant value in both ecology and economy. In order to delineate the extent of tidal flats at a large-scale by remote sensing technology, the Radial Sand Ridges (RSR) near the coastal area of Jiangsu Province was selected as the study area. Muti-temporal satellite images, which included Chinese HJ-1A/1B and Landsite series satellite images, were used as the data source. Then, the outermost waterline method was conducted to map tidal flats of the RSR from 2009 to 2017. Finally, the spatiotemporal dynamic change analysis was implemented. The results showed that from 2009 to 2017, tidal flats of the RSR decreased by 219.83 km², a loss of 8.7%. From 2009 to 2014, the area of the tidal flats increased by 8.35 km². While, from 2014 to 2017, tidal flats in the RSR declined by 228.88 km², with a loss of 9.18%. Tidal flats in the northern and southern part of the RSR showed the trend of erosion. Additionally, tidal flats in the inner and the middle part of the RSR flushed and silted alternatively. Our method enables to quickly monitor tidal flats with complex geomorphology and large scale, providing data reference for rational development and utilization of tidal flat resource in Jiangsu Province.