In this paper,a primary design of an Oscillating buoy wave power Device(OD) is conducted firstly,then a numerical calculation is carried out to find the main parameters that affect the performance of the OD,and find the optimal parameters of the OD when it works in South China Sea.The result shows that the length of the forepart of the port(Lf p) and the length of the buoy(Lb) are the primary parameters that affect the performance of the OD;the draft of the buoy(D) and the water depth in the port(Dp) are the secondary parameters,the performance of the OD can be improved partly by adjusting them;and the water depth in the region of constant depth(H) is irrelevant to the performance of the OD,It means that the water depth in the region of constant depth(H) can be left out of account when selecting a site to build the OD.The optimal parameters are shown below:Lf p=4 m,Lb=3 m,D=2.5 m,Dp=4.3 m around the usual wave period of 5-6 s in South China Sea.