Abstract China has become the world's largest carbon dioxide emitter and energy consumer, with serious environmental problems. Therefore, low-carbon economy has become the best choice for its development. In this paper, the economy, society, energy and environment are taken into account to build a low-carbon economy system (LCE). It is used to analyze the drivers of CO2 emissions and impact of low-carbon transition in China. Bayesian network and scenario analysis are applied. The results show that the increase of per capita consumption expenditure, energy consumption per unit of GDP, energy consumption per capita and CO2 emissions per capita is the reason for the continuous growth of CO2 emissions; the improve of energy efficiency, CO2 emissions per unit of GDP and CO2 emissions per unit of energy consumption inhibits CO2 emissions. China's low-carbon development does not come at the expense of its economic growth. Actually, the low-carbon transition is accompanied by the growth of population, consumer spending, energy consumption and energy efficiency. Urbanization rate will be up to 75.70%–97.44%. Compared with 2017, energy efficiency increases by 4.51%; energy consumption per unit of GDP reduces by 0.4%. Transformation of energy subsystem is the key to a low-carbon road.