Abstract: Firstly, fermentation conditions for lactase by Enterobacter sp.SYA2 were optimized by single factor experiment, the result showed that the optimum temperature was 37℃, liquid volume in flask was 50mL /250mL, vorotation speed was 175r /min, inoculation volume was 5% ( V/V) , seed age was 8 hours.Then Plackett- Burman design and Box-Behnken Design were combined to optimize the medium components of lactase production.The results showed that the optimal medium were as follows:lactose 31.1g /L, peptone 26.0g /L, yeast extract was 5.0g /L, K 2 HPO 4 3.0g /L, NaCl 6.0g /L, MnCl 2 0.5g /L, initiation pH was 6.5. After optimization, the lipase activity was 15.95U /mL.