For offshore wind power, the comprehensive cost-benefit assessment is the basis of planning and construction. Unreasonable planning will bring huge economic losses. In this regard, an improved VIKOR evaluation method integrating Vague set is proposed to evaluate the comprehensive cost-benefit of offshore wind power, including the life cycle cost, benefit from electricity sales, environment and carbon tax. First of all, a life cycle cost (LCC) model of offshore wind power is introduced to realize the separation of various cost, fully considering the impact of various cost indicators on the comprehensive cost-benefit of offshore wind power. Then, benefit indicators are established from the perspective of electricity sales, environment and carbon tax. On this basis, the improved VIKOR method is used to evaluate the offshore wind power schemes based on different grid connection modes, with the Vague set used to calculate index weight, and the optimal grid connection scheme is given. Finally, a typical offshore wind farm example is given to verify the feasibility and effectiveness of the proposed evaluation method.