This paper examines the objective，approach and means of the Obama Administration in facilitating the negotiation and the entering into force of the Paris Agreement focusing on greenhouse gas（GHG）emission reduction. Obama has repeatedly stated that the US goal is to play a leading role in responses to global climate change. That “leadership” has different definitions and policy implications in different periods. Obama’s “leadership” in the early stage mainly stressed improving the competitiveness of clean energy and promoting clean technology and its industrial development while the “leadership” in his second term directly manifested in its progressive climate diplomacy to promote global climate governance. The Obama Administration not only shapes climate change as a priority issue in the domestic political agenda，but also makes the climate issue as a focus issue of US foreign relations，particularly in pushing the climate issue into the US-China bilateral core political agenda—Strategic and Economic Dialogue. The Paris Agreement adopts Intended Nationally Determined Contributions（INDCs）to reduce global GHG emissions in a “bottom-up” approach，which is similar with the voluntary approach the United States has long been advocating.