Abstract: By using 1,4-two methoxyl glucopyranose as model molecule,the bond cleavage reactions of glucopyranose in cellulose and their thermodynamic properties at 298.15K and 363.15K have been investigated using density functional theory at B3LYP/6-311++G** level.The calculation results show that the two C—O bonds connecting the twohydroxyl group at C2 and C3 positions have the largest dissociation energies,much larger than other bonds,whereas the C4—C5 bond energy is the smallest in line with its longest bond-length.The C1—O4 glucosidic bond energy is larger than that of the C4—O4 glucosidic bond by 16.92 kJ/mol.In view of activated Gibbs free energy,the four preferential cleavage bonds are the C4—O4 glucosidic bond,the C5—C6 bond with dehydroxymethylation,the C4—C5 bond with the pyran ring opening and the C1—O4 glucosidic bond.It is very interesting that the C5—O5 bond cleavage accompanied by the breaking of the C1—C2 bond was found.So,the simultaneous cleavages of both the C5—O5 and C1—C2 bonds were further investigated.The results show that this pattern of bond cleavage yielding 5-member carbochain double radical immediate and another pyran ring formate,is much easier to take place than others in view of whether dissociation energy or Gibbs free energy.Based on this,the possible formation mechanisms of some signal molecules,such as CO/CO2,furaldehyde and methanol in ageing degradation of cellulose,were proposed.