Abstract: Sea level change is not uniform on the global scale. It has significant regional characteristics. The regional sea level change has more direct impact on people. The South China Sea, surrounded by mainland China, Taiwan Island, Philippines islands, great Sunda Islands and Indochina Peninsula, is the largest marginal sea in the equatorial region. The changes in the South China Sea have an important impact on these surrounding countries and regions. Many scholars have studied the sea level change in this area. In this paper, ocean mass variations in the South China Sea are estimated by the Gravity Recovery and Climate Experiment (GRACE) satellites and steric-corrected altimetry from-2003 to 2012. And then, the effects of El Niño-Southern Oscillation (ENSO), net freshwater flux, water volume transport and runoff on the ocean mass in the South China Sea during the period are discussed by using oceanographic and meteorological data. The results show that ocean mass variations in the South China Sea was dominated by sea surface net freshwater flux and sea water volume transport between the South China Sea and its adjacent seas, and the role of runoff from rivers nearby was limited. Oceanic mass variations in the South China Sea have significant seasonal characteristics with the annual cycle and a long-term increasing trend. ENSO made the ocean mass in the South China Sea change with a significant inter-annual characteristic through controlling precipitation and Kuroshio water volume transport though the Luzon Strait. The ocean mass in the South China Sea decreased during El Niño and increased during La Niña, and the size of changes were closely related to the intensity of ENSO event.