Abstract: Offshore wind energy development and utilization play an important role in haze governance and fulfilling the reduction commitments in advance. The reserve estimation of offshore wind resource in China is abundant enough to meet basic needs for the exploitation of wind power. Recently, more and more attention is paid on accurate estimation of offshore extreme winds, which impose important impacts on wind turbine design and operation. Different from numerous studies of typhoon extreme winds, the study of offshore extreme winds over the mid-high latitudes is significantly deficient due to the lack of effective methods, which is also a key area for the exploitation of wind power. Therefore, based on numerical modeling and spectrum analysis, the present study develops a practical, reliable and robust method for the estimation of 50 year extreme winds. This method can be applied to various mid-latitude offshore areas in China. Taking into account the complicated climatic characteristics of China's mid-latitude offshore areas affected by high-latitude cold winter winds and tropical cyclones, the 50 year return wind speeds at 100 m height over the offshore area of Jiangsu are estimated using this new method. It is shown that:(1) affected by strong cold winter winds, the 50 year return wind speed in the northern part of Jiangsu offshore area exceeds 40 m/s; (2) the 50 year return wind speed of 40 m/s (or even 44 m/s) near Xiangshui and Rudong is related to limited typhoon activities; and (3) the 50 year return wind speed over the central Jiangsu offshore area is generally lower than 35 m/s. This study not only provides a scientific basis for the design and operation of offshore engineering, such as offshore wind farms, but also contributes to further in-depth understanding of extreme climate events in China as well as the development of atmospheric boundary layer theory.