We establish a three dimensional current field using Mike3 Flow Model in the Beibu Gulf. The accuracy is verified by comparing the current data with the measured data of an offshore oil platform. We calculate the wind-tide coupled current by adding the daily mean wind field. On this basis and decoupling the Particle Tracking Model, a water exchange matrix is built. After doing the Lagrange particle tracking experiment, we get the tracking of the particle, the water renewal rate, mass transport paths and the average water residence time (ART) of each part of the matrix as well as the Gulf. The most active part in the Beibu Gulf is the southern border and the ART is 11.74 days. Subsequently, the ART of the Qiongzhou Strait is 16.15 days. However, the most inactive part is the coast of the Guangxi Province, and the ART is 79days. For the whole gulf, the ART is 77.88 days.