| With the rapid development of science and technology, the world agriculture has been developed.From the invention of pesticides and fertilizers to the emergence of genetically modified foods, biotechnology is changing people's lives and also plays a key role on agricultural output.But with the rapid increase in rural, inefficient operation of the agricultural economy, lacks of vitality of the rural economy, and the irrational using of agricultural resources, the phenomenon of agricultural pollution and the worsening situation exists to varying degrees in many regions of China.These problems force people to have to re-examine and adjust the relationship between man and nature,and the directions and ways of agricultural development.The sustainable development of agricultural is the object of study which concerned by the ecology, economics scholars.The emergy analysis theory that founded by the famous American ecologist Odum is the new results of the development of systems ecology and ecological economics,the theory overcomes the defects of the traditional economics which just study the economic value while ignore the value of resources and environment and the the lacks of traditional ecological system analysis method of value measurement,and the theory systematically considers the effects of the factors economic, resource and environment and so on in the ecosystem.Using the emergy analysis theory and method, people can convert different types energy that can not compare to the same standard emergy. It quantitative analyses the structure and function of the agro-ecosystem,it evaluates and analyses system's sustainable development capacity,and it opens up new ways and methods for the study of sustainable development of ecosystems.This paper applies the emergy analysis theory,it takes Hunan Agricultural ecosystem as the research object,and it analyses Hunan agricultural input and output, operation efficiency and environmental load based on the investigation, determination, calculation, collection of the information of natural resources, economic and social aspects of the system;It compares the system's level of development between different regions;It accounts of the city's sustainable development indicators --- Green GDP and sorts them; It analyses and reveals the emergy of the system's succession law and the basic trend;With the emergy sustainability index and the DEA method,it takes a comprehensive evaluation of the sustainable development status of the system. The main findings of this paper are as follows:①Hunan Province is an agricultural populous provinces,Hunan agriculture remains at the traditional agricultural phase which is maintained by a large number of labour emergy, although the emergy input is above the national average, but with the low level of mechanization and the low level using of environmental resources,agricultural ecosystems is relatively underdeveloped.②Hunan leading industries are agriculture and livestock farming, forestry and fisheries account for a very small proportion.In the planting industry, grain and oil crops are still dominant, other industries have not yet become a competitive advantage.From the view of net emergy yield,industry rate of return is not high.The main reasons are the low value-added agricultural products, and the industrial competitiveness is not strong.③From the view of environment load ratio, environmental resources withstand high pressure, but compared with developed countries it still has some room for growth.④After 10 years of Hunan agricultural development,agro-ecosystems of the input-output ratio has greatly improved, because Hunan agricultural ecosystem emergy input structure and the structure of the emergy output have been significantly changed.⑤The emergy flow between different agro-ecological zones of Hunan have considerable differences,and emergy analysis indicators'are quite different,there are obvious regional differences.⑥There are drawbacks and deficiencies for accounting methods of traditional agricultural eco-economic systemGDP,Green GDP reflects the sustainability of agricultural ecosystems better.Using the energy analysis method, this paper calculates the green GDP of the various states in Hunan province,and sorts the per capita green GDP of them,the results are different from the traditional GDP accounting and ranking results.⑦The reason why sustainable development of agro-ecosystem level is not high is that it has higher environmental loading rate but lower net energy yield.⑧the level of sustainable development of Hunan Agricultural eco-system is demonstrated as non-equilibrium, In this paper,the system level of the sustainable is comprehensively evaluated and ranked by the emergy sustainable development indicators, green GDP and DEA models. as a result:the highest scores for the top three sustainable development level is Zhuzhou, Changde and Chenzhou, the other as follows:Changsha and Yueyang, Yongzhou, Zhangjiajie Hengyang, Huaihua Xiangtan, Western self-Chau,Yiyang,Shaoyang, and Loudi.Finally, this paper puts forward countermeasures and suggestions for the sustainable development of Hunan:①We should optimize the input structure of the supporting energy, especially increase the elements of agricultural science and technology input,increase the level of agricultural mechanization,extend the industrial chain and so on,to improve the efficiency of agro-ecosystems;②We should control the number of rural population, improve the quality of rural population, and train new farmers;③We should speed up the urbanization process,transfer rural surplus labor force, and reduce pressure on the environment;④We should adjust industry and product structure and promot agricultural ecological and economic benefits;⑤We should implement differentiated agricultural industrial policy for different types of agro-ecosystems;⑥We should improve the utilization of agricultural resources,strengthen ecological environment construction,to promote sustainable development.
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