Abstract: In view of the continuous expansion of marine aquaculture in Sansha bay, the monitoring of marine aquaculture plays an important role in the management of marine fisheries and also provides a valid method to evaluate the expansion intensity of the mariculture.Based on Landsat TM/OLI remote sensing images from different periods, the mariculture area of Sansha bay in 2003, 2005, 2008, 2011, 2013, 2014, 2016 were extracted and counted in this study by using the support vector machine classification method, and the the expansion intensity of mariculture in the study area were evaluated through different expansion indicators.The results showed that:(1) during the period from 2003 to 2016, the area of cage and algae culture in Sansha bay expanded rapidly, the rates of expansion were 1.7 km²/a and 9.3 km²/a, respectively; (2) In 2016, the total area of marine aquaculture in Sansha bay reached 160 km² in 2016, exceeding 21.2% of the planned mariculture in Sansha bay; (3) Between 2003 and 2016, the expansion intensity of cage and algae culture varied greatly in different periods.The scope of cage culture developed from the mainland and the coastal of islands to the deep sea, the expansion scope of algae culture covers almost the entire sea.