The coastal tidal flat wetlands are facing the threat of degradation due to increasing human activities. During the past 30 years, the rapid economic development in the urbanized areas of eastern China led to great changes in the temporal and spatial pattern of coastal wetlands. Employing the high-resolution remote sensing images provided by Google Earth Pro (GEP) and Google Earth engine (GEE) platform, the wetland remote sensing images of China from 1990 to 2020 were interpreted and the spatial distribution map of coastal wetlands in the past 30 years was obtained. Combined with the relevant policies, this paper further studied the temporal and spatial patterns and mechanism of China coastal tidal flat wetlands in the past three decades. The results indicated that the total area of the coastal tidal flat wetlands in China had a decreasing trend in the past three decades, reducing by 42.98%. The area of the bare tidal flat reduced by 46.30%, while that of the vegetation area increased by 4.95%. The overall change in different provinces was in consistent with the national trend, which was affected by the national policy. However, due to different development needs and pressures in each province, the progresses of change varied in their tidal flat wetlands. The sediment deposition and hydrodynamic environment were the main natural factors that drove the changes of China's tidal flat wetland, while policies and guidelines were important human factors. The introduction of strict and reasonable control policies can promote the sustainable development of coastal tidal flat wetland in China.