In this study, the strain Trichoderma reesei SEMCC-3.217 was used for producing cellulase in solid-state fermentation with water hyacinth ( Eichhornia crassipes ). The results of fractional factorial design showed that, the addition amount of wheat bran, (NH 4 ) 2 SO 4 , CaCl 2 and Tween 80 had significant effect on the cellulase production. Then, these four factors were selected for further optimization by central composite design for the yield of cellulase. The statistical analysis of the results showed that, the optimum composition were: 5 g of substrate containing 3.9 g water hyacinth, 1% corn steep liquor, 1% soybean meal, 0.2% NH 4 NO 3 , 0.2% KH 2 PO 4 , 0.08% MgSO 4 ·7H 2 O, 2.8% (NH 4 ) 2 SO 4 , 1.5% urea, 13.9% wheat bran, 0.08% ZnSO 4 ·7H 2 O, 0.08% FeCl 2 0.05% CaCl 2 , 0.08% NaNO 3 , 0.08% KCl and 0.27% (v/v) Tween-80. Under these conditions, the cellulase production was 4-fold increased (13.4 FPIU/g dry solid) compared with the initial level (3.4 FPIU/g dry solid) after 7 days of fermentation in a 250 ml Erlenmeyer flask. Key words : Cellulase, solid-state fermentation, optimization, water hyacinth, Trichoderma reesei.