This paper uses a model of rising divergent mantle flow and convection coupling to simulate the expansion of eastern sea basin of the South China Sea, the ridge jump, and the process of lithosphere hot structure evolution and melting of magma after expansion. The results indicate that the ridge jump is an important process of the South China Sea expansion. Ridge jump forms a magma chamber between the two ridges, and the existence of the magma chamber makes the submarine volcanoes relatively more and also the terrain relatively high between the ridges.