Mangroves provide a variety of irreplaceable functions such as coastline protection, bay improvement, water purification and wetland diversity protection. However, mangroves are fragile ecosystems and are affected by human activities and climate change. Long-term monitoring on mangroves is of great significance. This paper selected Tongming Bay located in southern China coast as a study case because of its high variation of mangrove extent. Satellite remote sensing images from 1978 to 2018 were used for mangrove extent interpretation, and to obtain the distribution, changes, and main driving factors of changes in the Tongming Bay area in the past 40 years. The results showed that the area of mangrove extent in Tongming Bay continued to shrink from 1978 to 2013, and the area gradually increased after 2013. The main driving factor for the reduction of mangroves was the artificial aquaculture occupation of mangrove habitats, and mangrove area growth was mainly caused by artificial planting. The results of this study can provide references for local government on mangrove management and ecological restoration.