Abstract: In order to increase the lipid productivity of microalgae Chlorella sp. U4341,optimization of mixotrophic cultivation condition was carried out by response surface methodology. The optimal carbon and nitrogen sources for Chlorella sp. U4341 were glucose and sodium nitrate,respectively. Two most important influencing factors for lipid productivity of Chlorella sp.U4341 were screened via Plackett- Burman experiment.Subsequently,the steepest ascent experiment was used to guide key factors to approach the maximum lipid productivity region. Optimal concentrations of the three influencing factors were confirmed by central composite design and response surface analysis,and the results were 25.34 g·L- 1of glucose,1.67 g·L- 1of sodium nitrate. Cultivated with the optimized condition,the lipid productivity of Chlorella sp. U4341 reached 280.57 mg·L- 1·d- 1,which was increased by 54%compared with the original cultivation condition.