A treatment process featuring modest conditions (atmospheric pressure, moderate reaction temperature) was designed to fractionate lignocellulose into cellulose, hemicellulose hydrolysates, and lignin by formic acid based on corn cobs. A central composite design with four independent variables (formic acid concentration, catalyst dosage, reaction temperature, and reaction time) was employed to study their simultaneous effects on three responses, including hemicellulose sugars recovery, the ratio of delignification, and the cellulose content. The regression analysis performed on the experimental data indicated that the regression coefficients of determination (R2) were good for the second-order models. The experimental results showed that under optimum conditions (formic acid concentration, catalyst dosage (v(FA)/v(HCl)), reaction temperature and time were 85 wt%, 185:1, 65 degrees C and 6 h, respectively) the recovery ratio of hemicellulose sugars was 87.6%, the ratio of delignification was 66.3%, and the cellulose content in the residual solid was 76.8 wt%.