China and the United States have recently released their post-2020 CO_2 emission reduction targets under their Joint Announcement on Climate Change. To have a better understanding of the commitments of the two nations, we calculate and compare the efforts and/or actions that the nations would need to take to achieve the targets in terms of carbon intensity reduction rate of the economy,scale of new and renewable energy applications, the development stage where CO_2 emission would need to peak,and power sector decarbonization rate. We have found that, under the circumstances of above two countries to honor their commitment, China would need to have a higher rate of reduction in carbon intensity of the economy (annually around 4%) which is higher than United States (annually around 3. 59%) based on its 28% target. China would also need to take more accelerated efforts to promote new and renewable energy development and deployment than the United States. China's new and renewable supply will need to maintain an annual growth of 8% on average, and reach 1. 16 billion tons of coal equivalent (tce) in 2030,approximately twice of the amount in the United States. China will also need to achieve its CO_2 emission peaking in an earlier development stage and at a much lower per capita CO_2 emission (about 8t/person) than the United State did (19. 5t/person). It is projected that China will need to lower the carbon emission per kWh in its power sector by 35% from 2011 to 2030 to achieve its target while the United States only by 20% over the same period. According to our comparative analysis,China's post-2020 CO_2 emission reduction target is very ambitious and challengeable to achieve. The government should to take positive efforts to achieve this target. The efforts not only includes to strengthen and to refine the development planning of new and renewable energy,to decompose the reduction target and action to provinces and cities, but also includes promoting energy saving and improving technological innovation of new and renewable energy. After coordinating the economy, energy and the environment in rapid economic and social development, China will early realize low-carbon development and ecological civilization.