Achieving low-carbon energy transformation is vital for coordinating economic growth and environmental improvement to satisfy the carbon emissions peak and carbon neutrality targets. Existing studies, however, have been dominated by the mere exploration of the low-carbon transformation pathway with little consideration of the importance of energy substitution in low-carbon transformation. Doing so is believably unable to gain the double dividend effect for the economy and environment. Accordingly, this paper develops three energy-target scenarios, taking into account energy structure, electrification level, and carbon mitigation targets by 2030 announced by the Chinese government. A dynamic multi-sectoral computable general equilibrium model, CHINAGEM, is employed to examine the economic and environmental effects under different pathways of long-term low-carbon transformation. Firstly, we detect that China's primary energy consumption and electricity production structure would substantially transfer to low-carbon and clean along with all three energy-target scenarios. Secondly, due to the anticipated decline of fossil energy consumption, especially coal consumption, China's CO2, SO2, and NOX emissions in 2020-2030 would also possibly vastly abate with all the scenarios. Besides, it is highly conceivable for China to achieve its peak carbon emission of 12.4 GtCO2 in 2028 if it serves the comparatively more stringent low-carbon transformation pathways. Lastly, different pathways would also produce varying positive impacts on China's macro-economy and achieve the different extent of double dividend effects. The research concludes with a recommendation of tentative improvement policies towards low-carbon transformation under the carbon peak and carbon neutrality goals, including promoting energy substitution, renewable energy development, and low-carbon technologies.