Abstract: There are more than 6500 coastal islands being up to 500 m² in the vast sea area of China. The coastline of islands adds up to 1400 km, and the area amounts to 80000 km². Coastal islands play a very important role in location, resources, national defence, politics and so on. Especially waters around islands are rich in densely distributed marine resources, which is of benefit to developing the economy of coastal islands. With the development of marine resources, coastal islands have made great progress in economy. Through the study on the classification of economic type of 12 coastal island counties in China, we know that they belong to different stages of economic structure, this provides scientific basis for rational distributing industries of coastal island counties according to their local conditions, and also for adjusting their industrial structure in the process of economic development. Applying the method of “three axis map”, we study the dynamic thrack of structure’s core of three sectors of coastal island counties and analyse the development process of their structure of three sectors dynamically and quantitatively, get relatively good results in classifying economic types of coastal island counties.