1. It has been proved by investigations since 1959 that there exists a transversevertical circulation system in the Dong Hai. 2. This circulation system consists of the surface rip current (the divergencecaused by wind in surface water), the subsurface current of the Kuroshio climbingup along the bottom towards the shore and the upwelling near the shore. The lattertwo are partly caused by meridional currents in the lower layers. 3. The subsurface water is short of dissolved oxygen, so it is able to drive fishshoal to the fishing ground. It plays an important role in the process of concentratingfishes. Besides that, the effects of upwelling and other suitable conditions make thewestern bound or the circulation system have the opportunity to form a fishing ground. 4. Based on the fundamental priciples of circulation, wo can apply the informa-tion of the circulation in a certain period to the fishing forecasts, in order to make thearrangement of fishing and the operation on the ground.