Subsea long distance power line communication is the most widely used and the most economical way of communication in deepwater oil and gas development. Deep understanding and reasonable application of the transmission technology is important to ensure the quality of long distance operating and monitoring system of subsea control system. Based on the basic configuration of subsea control system, we analyze the mechanism of long distance power line communication and the influencing factors of communication attenuation. Combined with a subsea gas field project in the South China Sea, the calculation of communication loop maximum attenuation value, the communication effectiveness analysis and the calculation of umbilical key electrical parameters requirement are carried out. This study provides an effective method for the communication design of subsea control system, which lays a solid foundation for the design optimization and equipment selection of communication system of ocean engineering projects.