Marine ecosystem plays a vital role in the economy and society because of its service and production function. Marine ecosystem always changes under the pressure of climate change and human activities. We concern about the status and future of the ecosystem,but it is very difficult to assess and predict the ecosystem health condition. Marine biodiversity is one of the very important indicators of the marine ecosystem change. We focus not only on species composition and quantity change of marine organisms. It is important to determine which are the main contributors to the structure and function of the ecosystem. According to the function of various plankton species in an ecosystem,they can be divided into different functional groups based on the similarity of their ecological roles. By studying the changes of the functional groups,we can enhance our ability to understand the structure and function of ecosystem,and to predict the trend of ecosystem change and the resultant effect on marine biological resource and environment under the multiple pressures of global climate change and human activities. This will help us to establish the marine ecosystem based management.