Alien invasive algae along with ship ballast water have posed a serious threat to China’s marine ecological security. A clear understanding of the geographical distribution of invasive species and their response to climate change can provide a scientific basis for their prevention and control. In this study, combined with environmental variables and distribution data, MaxEnt was used to predict the potential geographical distribution and change trend of Alexandrium in the four major sea areas of China currently, 2040s (2040-2050) and 2090s (2090-2100), reveal the dominant environmental factors affecting the geographical distribution, analyze the migration trends of centroids the highly suitable area, and clarify the key control sea areas. The results showed that: 1) The AUC values of all models were significantly higher than random models, and the Kappa statistics of all models were higher than “general”, demonstrated that the prediction results were available. 2) The most important environmental variable affecting the geographical distribution of Alexandrium was the Temperature. Range (bio24), and its suitable range was 23.43-31.52ºC. 2) At present, in the corresponding sea areas of Nantong, Yancheng, Ningbo, Jiaxing, Dongying, Binzhou, Cangzhou, Tianjin, Tangshan, Qinhuangdao, Shenzhen, Dongguan and Zhongshan, special attention should be paid to the control of Alexandrium. 3) Under the future climate change scenarios, excepted in the South China Sea, the total and highly suitable area of Alexandrium showed an increasing trend. 4) Under climate change scenarios, in the Yellow Sea, the centroids of the highly suitable area would move to the southeast. In the Bohai Sea and the East China Sea, the centroid showed a trend of moving to different latitudes and directions. In the South China Sea, the centroids of of the highly suitable area and total suitable area of Alexandrium would both move to the southwest. Our results can provide a theoretical basis for the prevention and control of Alexandrium.