The technology of underwater acoustic communication system and its engineering design play an important role in coastal development. The offshore underwater acoustic communication system consists of multiple transmission nodes. Each node is composed of buoy，mooring systems and communication systems. The buoy and mooring system has a significant impact on the signal of underwater acoustic communication，and the design of the buoy system and mooring system needs to consider the factors such as wind，water flow and water depth. In this paper，the development and existing problems of underwater acoustic communication system were summarized and analyzed. The stress model of buoy，gravity ball，anchor chain，anchor chain and so on in the mooring system of the communication node of the off shore water communication system were established. Cable length model and drag to length model were also established.