Abstract: The effect of bran content on cellulase production by Trichoderma reesei Rut C-30 was studied through adding bran in appropriate amounts and investigating suitable ratio of bran to microcrystalline cellulose by software of Design-Expert. The results showed that bran in appropriate amounts could accelerate the production of cellulase. The optimal conditions for cellulase production obtained by the design of rotation-regression-orthogonal combination were 12.23 g/L of microcrystalline cellulose and 23.50 g/L of bran.Filter paper activity and yield coefficient in 250 mL shake flask was 6.383 FPIU/mL and 521.913FPIU/g, respectively. Filter paper activity and yield coefficient in 7.5L fermentor was 6.807 FPIU/mL and 556.582 FPIU/g, respec-tively. Filter paper activity in shake flask and fermentor increased 14.247% and 17.403%, after optimization, respectively. Yield of cellulase decreased 6.584% and 4.005%, respectively. Filter paper activity were 1.953 FPIU/mL and 1.745 FPIU/mL, when replacing microcrystalline cellulose with dilute acid pretreated poplar and steam exploded poplar, respectively.