[Background] A strain of microalgae was isolated from the tropical sea of Hainan province, and it has a high growth rate and strong adaptability. The microalga was identified as Chlorella vulgaris. [Objective] To improve the growth rate of C. vulgaris. [Methods] Based on the formulation of “Ningbo University 3#” medium, organic carbon of C6H12O6 and CH3COONa were added for the autotrophic culture, mixed culture and heterotrophic culture, respectively, and also, the mixotrophy medium of C. vulgaris was further optimized. [Results] The mixed culture method with 6 g/L CH3COONa showed the highest growth rate of C. vulgaris, comparing with heterotrophic and autotrophic culture method. The optimal formulation of mixotrophy medium was as followed as 6 g/L CH3COONa, 20 mg/L (NH4)2SO4-N, 5 mg/L NaH2PO4-P, 3 mg/L FeSO4-Fe, 1 mg/L Vitamin B1 and 0.000 5 mg/L Vitamin B12. The biomass (cell density) of the “mixotrophy medium” was up to 4.20×107 cells/mL by the end of the sixth day, being 2.30 times higher than the cell density of “Ningbo University 3#” medium. [Conclusion] The mixotrophic mode is optimal to the cultivation of C. vulgaris as compared with other two cultivation modes, and the optimized mixotrophic medium significantly enhanced the biomass (P<0.01).