Lots of investigation and research have been carried out in the South China Sea (SCS), and many genetic models, such as extrusion model of Indochina Peninsular, back-arc extension model and subduction and dragging model of Proto-South China Sea (PSCS), have been proposed. However, none of these models is widely accepted because they don't fit with some geological phenomena. Due to its special tectonic location, the surrounding tectonic environment has undergone complex reorganization. Starting with the interaction of the three plates and in combination with the real data of SCS, the authors put forward a back-arc extension-sinistral shear model in this paper. It is considered that the SCS is a back-arc basin of PSCS northward subduction, and was triggered by the large-scale left-lateral strike-slip formed by the northward drift of the Philippine Sea Plate. The left-lateral strike-slip on the western margin of SCS caused by Indo-Eurasian collision changed the direction of spreading axis of the southwest sub-basin from nearly east-west to north-east direction. The evolution of the SCS and its adjacent area since the late Mesozoic can be summarized as the follows: 1) the Australian plate began to drift northward, and the Neotethys subducted northward in the early Cretaceous, leading to back-arc extension and the formation of PSCS; 2) From the end of Cretaceous to Eocene, the PSCS subducted northward, resulting in formation of continental margin rift; 3) In Early Oligocene, the large scale sinistral strike-slip on the western margin of the Philippine Sea plate triggered back-arc extension of SCS from east to west; 4) At the end of Oligocene, the rollback by subduction of PSCS resulted in the spreading axis jumping to the south; accordingly, it shifted from nearly E-W to NW direction by the influence of sinistral strike-slip on the west margin of SCS; 5) In late Early Miocene, SCS spreading was stopped by collision of Nansha-northern Palawan block with Cagayan Ridge.