Abstract: ZhuangHe NanJian coast is one of the most typical Cape Bay mud coasts in China, over the past century, along with human activities in the watershed and along the coast, the coastal landform has undergone complex evolution laws, it is of great significance to study the evolution of this kind of coastal landform. Used the bathymetric data and remote sensing images from five periods since 1938, studied the tidal flats and offshore slope evolution based on 3S technology. The results showed that: ①The area of tidal flats has been declining since 1938, and by 2023 the area had decreased by 85.74%, a total decrease of 49.68 km². Reclamation is the key factor causing its shrinkage. ②The whole subaqueous slope is in a siltation state, the average siltation thickness is 0.57 m, the evolution law of subaqueous slope on the scale of decades is complex, and the evolution trend of different stages is alternating, and the stability is poor; the isobath changes significantly, the 0m isobath retreated 0.47 km to the mainland, while the 2m, 5m and 8m isobath advanced 0.66 km, 0.99 km and 0.16 km to the sea.