Millennium ecosystem assessment（MA）was launched by United Nations Secretary-General Kofi Annan in June 2001 and was completed in March 2005. So far, the MA is the first international work program designed to assess the global ecosystem by synthesizing information from all kinds of sources. The assessment focuses on the linkages between ecosystems and human well-being and, in particular, on "ecosystem services". Based on the latest findings, three main contributions presented by the MA were expounded in this paper. ① Conducted a comprehensive global assessment of the world’s major ecosystems and its four main findings, which can provide substantial scientific basis for decision-makers to improve their decision-making processes concerning ecosystem management; ② Enriched the connotation of ecological research by pointing out explicitly that a change in ecosystems is closely related to human well-being, and placing the study of “ecosystem and human well-being” as one central task for current ecologists, which can lead the development of ecology in 21^st century; ③Established a framework to assess the interactions between ecosystems and human well-being, and a analytical approach to conduct multi-scale and integrated assessments. Though great achievements have been gained with the MA implementation, but many issues still need to be discussed or improved, including concepts, methods and data.