In order to compare the most suitable operation and maintenance (O & M) plans for offshore wind farms of different scales under different sea conditions, by the economic analysis model for O & M of offshore wind farms, various O & M plans combining Crew Transfer Vessel (CTV), Service Operation Vessel (SOV), self-elevating platform and helicopters are compared. The number of O & M teams for different O & M plans is designed for typical sea conditions in China, and the economic analysis is conducted. It is found that for offshore wind farms with good sea conditions and fewer wind turbines, the utilization rate of helicopters is lower, and the O & M plan only using CTV is more suitable.