Based on the first principles method of density functional theory, the adsorption models of ZnO(100) and ZnO(001) surfaces were established to investigate the adsorption and reaction mechanisms of CH3Cl on ZnO surface through considering the adsorption sites, adsorption energy, charge density, density of states and transition state. The simulated results indicated that the adsorption of CH3Cl on both ZnO(100) and ZnO(001) surfaces was chemical adsorption. When CH3Cl was completely adsorbed, a weak chemical bond was formed between Cl and Zn atoms on ZnO surface. The adsorption of CH3Cl on ZnO(100) surface was more stable because the adsorption energy (-0.57 eV) of CH3Cl on ZnO(100) surface was lower than that (-0.42 eV) on ZnO(001) surface. When CH3Cl was adsorbed on ZnO(100) surface, the peaks of state density formed by the 3p orbital of Cl atom shifted to the left and the peak value near the Femi level was diminished comparing with that before the adsorption of CH3Cl. Thus the bonding effect of CH3Cl on ZnO(100) surfaces was more stronger and improved the stability of the system. During the dissociative adsorption of CH3Cl, the C atoms in methyl radical can be adsorbed to O(2a) and O(3a) on the surface of ZnO(100), respectively. The adsorption energy of CH3Cl dissociation adsorption on Zn(2a)/O(2a) site was -1.09 eV. There were three resonance peaks between O 2p and C 2p orbitals on the left side of the Fermi level. It was proved that there was a strong interaction between C and O atoms. On the other hand, the adsorption energy for CH3Cl dissociating on Zn(2a)/O(3a) site was -1.02 eV, and there was a resonance peak of O 2p and C 2p orbitals on the right side of Fermi level, indicating that there was a certain antibonding interaction between C and O atoms. The calculation results of reaction path way showed that the transition state energy of CH3Cl dissociation adsorption at Zn(2a)/O(2a) site was 1.69 eV, while it was 2.06 eV at Zn(2a)/O(3a) site. Therefore, the dissociation adsorption reaction of CH3Cl tends to occur at Zn(2a)/O(2a) site and to form the stable structure.