Masan county is located in central Guangxi,where is a typical region of the southwest karst mountain areas of China.In this paper,an emergy analysis method was used to evaluate the structure and function of agro-ecosystem in Masan county,Guangxi.The results showed that the total emergy input was slightly reduced,but the emergy outcome was rapidly increased in the local agro-ecosystem from 1994 to 2004.The organic emergy input reduced obviously with the decrease of agro-labour and animal power,but still was dominated in the emergy inputof agro-ecosystem.And the none-organic emergy from chemical fertilizer and pesticides was rapidly increased.The structure of system output emergy has changed from coexist by stockbreeding and planting to dominated by stockbreeding alone within the past 10 years.In addition,the coupled degree of the stockbreeding and planting,stockbreeding's dependence on external forage has strengthen slightly.In general,the emergy productivity of agro-ecosystem and the converting rate of the micro-economic value in this karst mountain county are still relatively low,which indicated that the development of agro-ecosystem was placed in an unstable and unsustainable status.Therefore,some strategies and suggestions were put forward to develop agro-ecosystem productivity,improve the structure and function of agro-ecosystem and enhance the comprehensive economic efficiency of agro-ecosystem.