The present paper reviews the UN important efforts to promote global sustainable development in the chronological order since UN Conference on Human Environment in 1972, and analyzes the progress and gap. The results show that the UN system has made great efforts for global sustainable development since the UN Conference on Human Environment, especially since UN Conference on Environment and Development, promoted the formation of important consensus and multilateral international conventions on many fields, boosted the development of partnership in the field of sustainable development, and accelerated actions for sustainable development of many countries and regions. However, at present, the progress made is still far below the level required, prominently reflected in the slow progress toward the millennium development goals, the difficulties in negotiations in the field of environment and development, insufficient fulfillment of international agreements and conventions, and undesirable effects of partnership in the field of sustainable development. Based on these, the paper puts forward four suggestions for UN Conference on Sustainable Development in 2012(Rio+ 20): (1) to revitalize the "spirit of Rio" and accelerate the implementation of existing political commitments; (2) to make new political commitments focusing on climate change and other major global challenges under the Rio principles; (3) to lay out a blueprint of green economy under the Rio principles; and (4) to promote South-South cooperation as the focus of international cooperation.