This study analyzed historical hydrographic data consist of 95 years of NODC data and 18 years of NCOR data. Variations of upper-layer current in Luzon Strait and its neighboring Northern South China Sea are investigated by the method of dynamical topography. On the other hand, higher salinity characteristic of the North Pacific Tropical Water (NPTW) is used to trace the water mass distribution and its seasonal variations in the studied area. The result shows that the maximum of x-component velocity (along 120.25˚E, relative to 400 m ) in the Luzon Strait occurs in the middle of the strait, the flow direction is westward and the speed increases toward the surface. At the north and south ends of the strait flows are eastward and the maximum speed core is at the depth of 0~50 m. Horizontal distribution of flow fields indicates that intrusion of the north Pacific waters into the South China Sea through the Luzon Strait in the whole year. Westward bifurcation of the intrusion flows occurs at 20~21˚N. A cyclonic eddy exists in the South China Sea all year-round, and its core is located at about 18˚N, 118˚E. This eddy strengthens as the monsoon prevails with its speed reached in January and February. Annual mean upper-layer transport (0~ 400 m) of the Luzon Strait is estimated to be about 3.5 Sv (positive value means westward) with a maximum value of about 6.5 Sv in December and a minimum value of 1.1 Sv in June. The Upper-layer current of the SCS is dominated by the monsoon. When the northeast monsoon prevails, the currents are affected by the Ekman effect to form high sea surface height in the north and low sea surface height in the south to produce a westward current. On the other hand, strong two coexistent wind stress curls with reversing signs during the northeast monsoon produce a westward current along the line of zero curl in the middle of the strait. The distribution of the NPTW(£m£c=23.5¡ã25.5 kg/m3,S >34.5 psu) is mostly at a depth of 120¡ã130 m in the South China Sea. NPTW were traced at 125 m depth, and the result indicates that this water mass enters the South China Sea through the Luzon strait all year-round. The intrusion path is along the continental slope of south China. The extent of intrusion reaches the maximum between December and February, and the water mass can spread into the South China Sea basin.