Abstract: Following criteria of sudden intensity changes in offshore tropical cyclones proposed by the experts of key projects office for the"8th five-year plan"in the national bureau,elassification statistics is done for the tropical cyclones in offshore Chinese waters 1970 through 1991 which meet the requirement.They all have the following climatic characteristics.There are in average 8-9 tropical cyclones per year whose intensity change abruptly as they move towards the offshore,among which 79.6% of the total weaken May through December while 20.4% intensity May through October;the former appears over vast area,while the latter is monthly seen over waters offshore the Zhejiang and Fujian Provinces,the central South China Sea,waters from the Pearl River Mouth across the Beibuwan Bay,and eastern Bashi Channel;No tropical cyclones enchance north of 30°N and west of 125°E or in the eastern South China Sea.