Abstract: Climate change has become a core challenge for human sustainable development, and low-carbon energy transition has become a key measure to mitigate climate change. Carbon emission reduction is one of the key benefits of energy transition. If the carbon emission reduction benefit can be evaluated monetarily, the cost-benefit analysis of alternative energy transition goals and paths with the unified currency dimension can be realized. This paper analyzes the mainstream monetary value evaluation method of carbon emission in detail, and proposes the social cost of carbon（SCC） as a more suitable method for the long-term energy transition problems. Furthermore, the sub-modules of SCC assessment are elaborated, including social economy, climate change,damage assessment and discounting modules, and the uncertainty sources of evaluation model are discussed. Finally, a typical SCC assessment model is chosen to calculate the country level SCC（CSCC） in China, and the sensitivity analysis of the key parameter（the discount rate） is provided, which can provide an evaluation methodology of carbon emission reduction benefit for the cost benefit analysis of alternative energy transition plans.