IPCC WGIII AR5 is developed in the context of deeply restructuring the strategic profile of the world's economy, energy, GHG emission, technologies, and the global climate governance, and when the new round of international climate talk, known as Durban Platform process, has been underway. Starting from a discussion on the different understandings of the storyline for the IPCC WGIII AR5, this paper reviews and explores varies of issues, including framing concepts for socioeconomic assessment of climate mitigation, historical trends and corresponding drivers of greenhouse gases emission trajectories, transformation pathways to achieve a target of temperature rise less than 2℃, institutional and policy options to support the pathway transformation, as well as evolution of knowledge system and methodologies for socioeconomic assessment of climate mitigation. Based on reviewing the key messages from WGIII AR5, the authors come up with several recommendations on developing China's strategy and policy options for its low carbon development and correct interpretation and application of knowledge and information from AR5 in the future studies on the socioeconomic assessment of climate mitigation in China.