The outbreak of COVID-19 pandemic has increased the production costs of renewable energy facilities and undermines the profitability of renewable energy investment. Green finance polices, e.g. carbon pricing, tradable green certificate (TGC) and green credit, can provide low-cost finances and counteract the adverse effects of COVID-19 pandemic. In this work, the generation costs of offshore wind power before and after the COVID-19 pandemic in China are analyzed using the data of 97 offshore wind power projects implemented in the period of 2014-2020, and the effect of green finance policy on the generation cost and the project profitability are evaluated. The results show that the average levelized cost of electricity (LCOE) of offshore wind power decreased from 0.86 CNY/kWh in 2014 to 0.72 CNY/kWh in 2019, while it increased to 0.79 CNY/kWh in 2020, i.e. 10.85% increase relative to that in 2019. With the average carbon price of 50 CNY/t CO2, the average TGC price of 170 CNY and the green-credit policy being introduced, the average LCOE decreases to 0.76 CNY/kWh, 0.67 CNY/kWh and 0.74 CNY/kWh respectively. The green finance policy mix is still necessary to support the offshore wind power investment during the Covid-19 pandemic.