Based on wind, wave height, temperature and humidity data, the optimized Kmeans algorithm which combines DB criterion and the method of maximum distance is used in China’s offshore climate regionalization in winterThe optimized algorithm avoids the drawbacks of subjectivity of determining cluster number and initial cluster centers in the traditional Kmeans algorithmThe results show that three regions are obtained: Region 1 mainly includes the sea area north of 28°N and the long narrow area in the southeast coastal of China; Region 2 mainly includes the circumjacent seas of the Taiwan Island, Taiwan Strait, Bashi Channel and most of the South China Sea from the southwest to the northeast; Region 3 mainly includes the sea area in the southwest of the Taiwan Island, Beibu Gulf, coastal areas of Guangdong Province and the southeast of the South China Sea By analyzing the climate characteristics of each region and their influences on ships and people on the seas, according to the regionalization criteria, we conclude that Region 1 is basically suitable for sailing, Region 2 is not suitable, and Region 3 is suitable