Degradation kinetics of hemicellulose of wheat straw pretreated by propionic acid was studied. The results showed that two distinct phases occurred during the degradation process of hemicellulose of wheat straw, the fast degradation stage from the beginning to 60 min and the mild degradation stage from 60 min to 180 min. The rate constant and the order of reaction were determined through the establishment of kinetic equation. Under the temperature of 60℃, 70℃, 80℃ and 90℃, the rate constants were 1.98×10-4、1.67×10-3、1.79×10-2 and 4.42×10-2 , respectively. At the same time, the order of reactions were 1.99, 1.40, 0.61, 0.46, respectively. The experiment was carried out in a certain range of temperature and time, the average active energy was 180.16 kJ/mol, and the frequency constant was 5.27×1024L/（mol·min）.