Utilizing a fixed-effects model and the Difference-in-Differences method, this research delves into the significant impacts of Offshore Wind Power development on China's marine economy, based on data from 2006 to 2019 across 11 coastal provinces. The findings reveal that with each 1 MW (MW) increase in the installed capacity of Offshore Wind Power, the marine output value rises by 58.71 million yuan. Further analysis shows that the Gross Domestic Product of the primary marine industry, encompassing sectors such as fisheries, grows by 4.2 million yuan. Concurrently, the secondary marine industry, which includes marine mining, sea salt, and chemical industries, sees an increase of 42 million yuan. The economic ramifications of Offshore Wind Power development are evident across three stages defined by installation capacity. In the initial stage, with installations below 1767.28 MW, the marine economy thrives. The intermediate stage, marked by capacities between 1767.28 MW and 3634.46 MW, faces challenges, mainly due to the coastal regions' limited capacity for integration. Conversely, the advanced stage, with installations surpassing 3634.46 MW, observes a revival in marine economic growth. Environmentally, the marine ecosystem encounters challenges during the installation phase but improves during the operational phase. Given these insights, it is recommended that China to expedite Offshore Wind Power development, refine its layout, and prioritize environmental conservation throughout its lifecycle.