Abstract: The South China Sea is located at the juncture of the Eurasian, Indian-Australian and Pacific plates and complicated in tectonic location and evolution. It has experienced a process from rifting of a passive continent to seafloor spreading, under the affection of both tectonic extrusion and asthenosphere upwelling. Based on the tectonic and dynamic background of South China Sea, a 2D finite element dynamic model with a pre-existing weak zone was prepared to explore the behaviors of the two dynamic forces. The simulation results indicate:(1) The lithosphere where faults or weak zones occur is easier to have stress concentration and crust thinning;(2) The asthenosphere upwelling seems play a more important role in the opening as the tectonic extrusion can hardly cause lithosphere's damage,;(3) The rheological properties may have greater contribution to the opening of South China Sea comparing to the existence of weak zone. The rheological properties of the lower crust may cause a greater crust thinning comparing to the upper crust.