BACKGROUND Selective hydrolysis of hemicellulose component from lignocellulose is one of the most vital steps for lignocellulose biorefinery. In this report, wheat straw, one of the largest output agriculture residues, was treated by high-pressure CO2-H2O in the presence of a low concentration of acetic acid to selectively hydrolyze hemicellulose. RESULTS Thein situformed carbonic acid and acetic acid catalyzed the selective hydrolysis of hemicellulose. The removal ratio of hemicellulose reached 82.3% when the lignocellulose was treated in the high-pressure CO2-H2O-CH3COOH (C-acetic acid= 0.3 mol L-1) system at 180 degrees C for 1 h, and oligosaccharides and monosaccharide were the main products. After removing most of the hemicellulose component, the cellulose component was exposed with the increase of surface area. Additionally, the surface of treated wheat straw became rough. CONCLUSION High-pressure CO2-H2O with low concentration of acetic acid is effective in removing and hydrolyzing the hemicellulose component of wheat straw. Acetic acid improves the removal ratio of hemicellulose. (c) 2020 Society of Chemical Industry