Introduction  The paper aims to study the cost composition and cost level of the offshore flexible DC delivery system and provide beneficial exploration for the cost control of the offshore flexible DC delivery system.

  Method  By collecting the design and cost quantities of the offshore flexible DC delivery system, we analyzed the costs of offshore flexible DC delivery system by using statistical analysis method, cost composition method and comparative analysis method.

  Result  The unit capacity investment level and investment composition of typical schemes of offshore flexible DC delivery system are given, and the key factors of cost level control of offshore flexible DC delivery system are put forward.

  Conclusion  The unit capacity investment of offshore flexible DC delivery system is 3,750~4,600 yuan/kW, and the costs, according to their component ratio (from high to low), are equipment procurement cost, construction cost, other cost and installation cost, and the systems, according to their component ratio (from high to low), are: marine converter station, sea cable, onshore converter station and other parts. Compared with the onshore flexible DC delivery system, the overall difference is about 1.3~1.6 times.