The existing estimates of the volume transport from the Pacific Ocean to the South China Sea aresummarized, showing an annual mean westward transport, with the Taiwan Strait outflow subtracted, of3.5±2.0 Sv (1 Sv=106 m3 s-1). Results of a global ocean circulation model show an annual mean transportof 3.9 Sv from the Pacific to the Indian Ocean through the South China Sea. The boreal winter transport islarger and exhibits a South China Sea branch of the Pacific-to-Indian Ocean throughfiow, which originatesfrom the western Philippine Sea toward the Indonesian Seas through the South China Sea, as well asthrough the Karimata and Mindoro Straits. The southwestward current near the continental slope of thenorthern South China Sea is shown to be a combination of this branch and the interior circulation gyre.This winter branch can be confirmed by trajectories of satellite-tracked drifters, which clearly show a flowfrom the Luzón Strait to the Karimata Strait in winter. In summer, the flow in the Karimata Strut isreversed. Numerical model results indicate that the Pacific water can enter the South China Sea and exittoward the Sulu Sea, but no observational evidence is available. The roles of the throughflow branch in thecirculation, water properties and air-sea exchange of the South China Sea, and in enhancing and regulatingthe volume transport and reducing the heat transport of the Indonesian Throughflow, are discussed. The existing estimates of the volume transport from the Pacific Ocean to the South China Sea aresummarized, showing an annual mean westward transport, with the Taiwan Strait outflow subtracted, of3.5 ± 2.0 Sv (1 Sv = 106 m3 s-1). of a global ocean circulation model show an annual mean transport of 3.9 Sv from the Pacific to the Indian Ocean through the South China Sea. The boreal winter transport is larger and exhibits a South China Sea branch of the Pacific-to-Indian Ocean throughfiow, which originatesfrom the western Philippine Sea toward the Indonesian Seas through the South China Sea, as well asthrough the Karimata and Mindoro Straits. The southwestward current near the continental slope of then northernhern China Sea is shown to be a combination of this branch and the interior gyre gyre. This winter branch can be confirmed by trajectories of satellite-tracked drifters, which clearly show a flow from the Luzón Strait to the Karimata Strait in winter. In summer, the flow in the Karimata Strut isreversed. Numerical model results that the Pacific water can enter the South China Sea and exittoward the Sulu Sea, but no observational evidence is available. The roles of the throughflow branch in the circulation, water properties and air-sea exchange of the South China Sea, and in enhancing and regulating the volume transport and reducing the heat transport of the Indonesian Throughflow, are discussed.