The efficient conversion of CO₂ into fuels and chemicals represents a key route toward sustainable biomanufacturing, and microbial cell factories offer significant potential for this purpose. Despite substantial advances in carbon fixation pathway design and carbon flux rewiring, the performance of microbial CO₂-fixing systems remains largely constrained by the efficiency of energy supply and utilization. At the core of this limitation is a systemic mismatch between energy metabolism and carbon fixation, involving discrepancies in energy carrier types [ATP, NAD(P)H, and low-potential electrons], supply ratios, and redox potential, which ultimately restrict carbon flux and energy utilization efficiency. From the perspective of energy-carbon flux coupling, this review proposes an energy conversion chain framework that conceptualizes carbon fixation as a cascade network comprising energy input, electron transfer, and carbon assimilation. On the basis of this framework, a quantitative evaluation system is established, encompassing energy input efficiency (EE), redox/electron utilization efficiency (RE), and energy-to-carbon conversion efficiency (ECE). By integrating experimental measurements with metabolic modeling, we systematically analyze the distribution of energy carriers and electron fluxes and identify key bottlenecks, including limitations in energy input flux, electron transfer losses, cofactor mismatches, and reaction network efficiency. At the engineering level, we further summarize strategies for improving energy-carbon compatibility, including chassis selection under energy constraints, construction of exogenous energy-supplying modules, and rewiring of endogenous energy networks. Building upon these advances, a multi-scale energy-carbon co-design framework is proposed to achieve precise matching between energy supply and carbon fixation demand. Overall, this review redefines energy metabolism as a central design dimension in carbon fixation engineering and provides both a theoretical foundation and engineering strategies for the development of efficient and robust CO₂ bioconversion systems.