With China's economic and social development, energy consumption and CO_2 emissions continue to increase, and the impacts of greenhouse gas emissions on the global warming are gradually intensifying. The long-term energy demand forecasting and the corresponding sustainable energy development strategies are the hotspot in present research. Following the idea of bottom-up' and top-down ,a medium- and long-term energy demand projection model is established by using such methods as dynamic material flow analysis, econometrics, and elastic coefficient and energy system optimization system. Based on the 2030 carbon emission peak target, the future energy demand and carbon emissions are forecasted under different carbon tax scenarios by choosing the carbon tax as the driving factor and designing three carbon tax scenarios. The result shows that China' s energy demand will reach the ceiling in 2045; the structure of primary energy demand will be dominated by non-fossil energy and the boost of renewable energy is the main driver of the transformation; electricity will become the largest final energy and play a dominant role in final energy consumption structure change.