Abstract: In order to improve the yield of dextranase biosynthesis produced by Penicillium cyclopium(CICC-4022),the cultivation conditions were optimized. The effects of liquid volume,fermentation temperature,initial pH and shaking speed on dextranase production were studied in the fermentation process by single factor experiments. On the basis of single factor experiments,the interaction and optimal combination of fermentation conditions were determined by response surface methodology. The results showed that the optimum conditions were determined as follows:Flask volume 60 mL/250 mL,fermentation temperature 30℃,initial pH of culture medium 6.0,and the shaking speed 160 r/min,the dextranase activity reached(53.68±0.12) U/mL,which was 30.10%±0.08% higher than before optimization.