Abstract: Microalgae can convert CO₂ into energy-rich organic matter through photosynthesis. With advantages such as high photosynthetic efficiency and no competition with food crops for arable land, microalgae-based carbon reduction technology is recognized as a key approach to achieving China’s carbon peaking and carbon neutrality goals. Light intensity and nitrogen availability are two crucial factors influencing the photosynthetic growth and metabolite synthesis of microalgae. While light provides the energy driving photosynthesis, nitrogen is essential for the synthesis of pigments—the cellular “light absorbers”—highlighting the need for coordinated regulation of light and nitrogen. Moreover, the optimal requirements for light and nitrogen vary with growth stages and target metabolite types. To achieve economically efficient carbon sequestration and organic matter production, this study proposes a light–nitrogen synergistic phased regulation strategy, in which light intensity is gradually increased and nitrogen is supplied in two distinct stages, based on the specific requirements of Chlorella vulgaris at different growth phases. The effects of this light/nitrogen phased control on the microalgal photosynthetic growth rate, CO₂ fixation rate, and organic composition were systematically investigated. The results showed that pigment content in microalgal cells was positively correlated with the initial nitrogen mass concentration. Under low nitrogen conditions （NaNO₃ mass concentration of 0.15–0.55 g/L）, lipid accumulation was favored, while nitrogen-rich conditions （0.75–1.05 g/L） led to higher protein and carbohydrate contents which increased by 20%. The maximum carbon dioxide fixation rate of microalgae was increased by 13% to 0.56 g/Ld by synergistic regulation of light intensity and nitrogen source mass concentration during microalgae growth. The maximum biomass concentration of microalgae increased by 14.78% and the percentage of oil quality increased by 36.2%, which realized the synchronous improvement of microalgae yield and productivity. Therefore, the coordinated regulation of light, nitrogen and energy proposed in this study is an effective method to improve the carbon fixation efficiency of microalgae.