Abstract:  With the development mode of deepwater oil and gas field heading towards intensification, subsea production system has more and more applications, and the power supply system develops from the original short distance one to long distance one. Based on the analysis on the subsea production system load, it is believed that long distance power supply for the underwater production mechanical dynamic loads is the main problem of underwater power supply. Taking the oilfield development in the South China Sea as the background, comprehensive exposition and analysis are given for the key technologies in long distance power transmission and distribution of the underwater production system, including key equipment selection, power computing technology, etc. In the case study, the mechanical power load power supply and the control load power supply are calculated, and related analysis is carried out.