The characteristics of the average monthly variation of the velocity distribution of water exchange across the 120°E section in the Luzon Strait is analyzed. The volume transport of this water exchange is calculated, the monthly and seasonal variation structure of the volume transport and its vertical structure are discussed based on the AIPO（The joining area of Asia and IndianPacific Ocean）data from 1993 to 2006. The results show that:①In the north-south direction of the section, the boundary of the westward flow is located at near 19.5°N, while the boundary of the eastward flow is located at near 21.5°N. The velocity distribution of the westward and eastward flows alternate, is characteristic of a two-in（west to flow into the South China Sea）two-out（out of the South China Sea）structure. The water of the South China Sea flows into the Pacific Ocean to the east direction each month throughout the year, in the area as deep as more than 300 m in south of 21.5°N, and less than 1 000 m in north of 21.5°N.②Almost all the net volume transports in the upper, the deeper and the full depth layers flow westward, which claim the largest in winter, followed by autumn and spring, and with a minimum in summer. The net volume transport of the middle layer is the largest in spring, followed by summer and autumn, with a minimum in winter.③The net volume transport of the entire section, features a sandwich structure in January-May and August-November, a two-layer structure in June and July, and a single-layer structure in December. Averagely within a year, the annual average structure of the net volume transport presents a sandwich structure.