China's high-speed railway (HSR) is booming recently, the HSR's performance of energy conservation and carbon reduction has attracted much attention. This study developed a new life cycle model of energy consumption and greenhouse gas (GHG) emissions on China's HSR by life cycle analysis (LCA), covering the stages of infrastructure, HSR train, and operation, based on the TLCAM (Tsinghua-LCA Model). A case of the Beijing–Shanghai HSR has been studied to show that the full life cycle energy consumption and GHG emissions of HSR transportation are 0.4 MJ km−1 per capita and 0.04 kg CO2e km−1 per capita, respectively, which are far less than aviation, gasoline vehicles, diesel vehicles, electric vehicles and public vehicles. With the cleaner power structure and the progress of HSR train technology, the energy consumption and carbon emissions of HSR in 2020 could be reduced by 20% compared to 2015. This study indicates that electricity generation mix structure and full load rate are important factors influencing the life-cycle energy consumption and GHG emissions of HSR transportation. It is recommended to improve the coverage of HSR network, accelerate train upgrades, improve the full load rate of HSR trains, and promote the low-carbon development of electricity supply to strengthen and realize the low-carbon advantage of HSR transport mode in China. HSR transportation can be used to achieve the low carbon transformation of China's transportation sector and improve oil supply safety situation.