[Objective] To interpret the effect of sodium lactate (a carbohydrate metabolite) on cell growth and astaxanthin accumlation during Phaffia rhodozyma fermentation, based on the metabolic regulation mechanism of astaxanthin synthesis. [Methods] The astaxanthin producing strain Phaffia rhodozyma JMU-VDL668 was cultured in shake flasks and 7 L bioreactor respectively. The effect of sodium lactate on the synthetic metabolic flow of astaxanthin was studied with the method of metabolic flux analysis. [Results] It was found that adding sodium lactate into 7 L bioreactor increased astaxanthin accumulation significantly, and the production of astaxanthin reached 17.70 mg/L, which was 26% higher than the production of the control group. The regulation mechanism of sodium lactate on astaxanthin synthesis was studied by means of metabolic flux analysis, and it was shown that sodium lactate could adjust metabolic flux distribution at the nodes of pyruvate and acetyl-CoA. Lactate was catalyzed by dehydrogenase and directly into later half of the metabolic network. Thus the flux of acetyl-CoA and the flux down to TCA cycle were significantly increased. [Conclusion] Adding sodium lactate during fermentation could provide more precursors (acetyl-CoA etc.) and energy, and so improved astaxanthin synthesis.