To solve the problem of underwater and long-distance transmission of ocean sensor data,a PLC long-line transmission circuit system is proposed. The system adopts power line communication (PLC) technology, CR600 as the control core, CR150 as the analog front end with chip control data receiving and sending. The data is transmitted back to the ground through the umbilical cord, and then the data is received by the ground control system and the upper computer,realize the ocean sensor data transmission. In order to ensure the normal operation of the circuit system in 1000 meters underwater, the pressure chamber is designed. According to the theoretical calculation and COMSOL simulation, the specific parameters of the pressure chamber are determined. It has been verified that the system works stably, the long-term data transmission is complete, and it can realize the long-term transmission of marine sensor data.