The offshore wind power is the most valuable renewable energy for large-scale development. The total?capacity of offshore wind power will be expected to exceed 8.5 GW by 2020 in China. The cost of operation & maintenance accounts for 25%-40% of levelized cost of electricity (LCOE). The government promotes the wind power grid parity since 2019, which will be far-reaching?effects on the development of offshore wind power. Based on the analysis of LCOE, a cost-benefit model is established. It is found that the reliability and availability of wind power equipment determines the level of the cost of operation & maintenance and LCOE. Based on the cost-benefit model, the lowest LCOE of one offshore wind power project is 0.5752 RMB/kW.h when the availability of wind power equipment is 97.15%, which the cost of operation & maintenance decreased by 26.88%.