In order to obtain the environmental data of offshore wind farm and study the local ecological effect on the surrounding sea area after the completion of its construction, a comprehensive survey of marine environment and biodiversity was carried out near Dafeng H12 wind farm in Yancheng, Jiangsu Province on September 25, 2020. Based on the measured data, the physicochemical properties, and marine organisms of the water inside and outside the wind farm are analyzed by the classification analysis and index of relative importance. The extracted information shows that the sea surface temperature inside the wind farm is lower than outside about 1.05°C. The quality of water environment decreased, and the turbidity increased significantly from outside to inside, about 4.29 NTU. The number and species of fish eggs, larvae and juveniles inside the wind farm are less than those outside, the dominance of benthos changed, and the abundance of catch inside the offshore wind farm was reduced. The construction and maintenance of offshore wind farm have changed the biological habitat. However, some alien species can adapt to the local ecological environment. This survey enriches the poor local environment database of offshore wind farms. This result provides a scientific basis for the construction of regional eco-environmental effect assessment system and the ecological restoration and protection measures under the influence of offshore wind farms.