Taken an offshore oil and gas field development projects in the Bohai Sea as the research object, a model of the total cost of electricity and carbon for the offshore oil and gas field development is established, the carbon emission and economic benefits of green power consumption under the onshore power mode of four offshore oil and gas field development projects are compared and analyzed, and the impacts of the price of green power and carbon trading on the economic benefits are elucidated. The results show that the total cost of electricity and carbon is negatively correlated with the proportion of green power consumption, green power consumption can reduce carbon emissions by about 80% on average, and the economic benefits of purchasing green power for offshore oil and gas field development projects are more obvious. As the carbon trading market and green power green certificate trading system tend to improve, there will be more room for economic benefit to rise. If it is considered that the environmental premium of green power consumption increases, the increase of green power price will have a negative impact on economic efficiency.