Climate change mitigation issues including China's carbon emission status, the mitigation potential and cost in different sectors, the target of 40%-45% reduction of emission intensity of GDP in 2020 compared with the 2005 level, and conditions and uncertainties of the carbon emission peak are analyzed and assessed in the Third China National Climate Change Assessment Report and summarized in this paper. Economic structure adjustment has played and is expected to continue to play important role for carbon mitigation. Development of nuclear and renewable power would contribute to around 2 billion tons and 3.7 billion tons carbon reductions by 2020 and 2030 respectively. Key energy saving and low carbon technologies in the end-use sectors such as industry, transportation and building are listed and assessed. The mitigation potential and cost curve for steel is provided as an example to show that a large amount of carbon emissions could be reduced with minus mitigation cost partly resulting to energy saved. For industry process, carbon mitigation potentials would be around 420 million tons and 770 million tons by 2020 and 2030 respectively. Carbon mitigation potentials from LULUCF (Land use, land use change and forestry) are still uncertain and needed further research. For the assessment of 45% carbon intensity reduction target in 2020, it is concluded that economic structure adjustment, energy efficiency improvement, development of non-fossil energy, building and transportation would contribute to 33.4%, 28.5%, 20.4% and 17.3% of the total reductions. Assuming GDP growth rate as 6%-7% during 2010-2030, energy intensity reduction rate as 15% during 2015-2020, 14% during 2020-2025, and 13% during 2025-2030, the total primary energy consumption would be around 6 billion tons. To control coal use to less than 50% of the total primary energy consumption, while increasing the share of nature gas to over 10%, and the share of new and renewable energy to 20% or higher, carbon emissions would peak around 2030 at 11 to 12 billion tons. Finally, Climate change mitigation strategies to facilitate the achievement of China's carbon emission peak target are proposed. It's also suggested that measures are needed to accelerate the economy restructuring and development modes shift, to control the growth rate of total energy demand, to maintain a sustainable energy system with the new and renewable energy as its main components, and to achieve the carbon emission peak target by sector and region.