Methyl parathion hydrolyse (MPH) could degrade methyl parathion efficiently, as well as fenitrothion, ethyl parathion and chlorpyrifos, with the degradation efficiency decreasing systematically. In order to improve the degradation activity of MPH on chlorpyrifos, random mutation was carried out by error-prone PCR. Two mutants A291V and K173R were screened and expressed in E.coli BL21(DE3). The degradation activity of K173R on chlorpyrifos increased 41.55% as compared to MPH. Besides, homology modeling and molecular docking were used for preliminary analysis of the relationship between the enzymes’ structure and function. The results showed that the residue R72 played an important role in combination with chlorpyrifos, and changes occurring in the binding pocket and key amino acids eventually led to the increased degradation efficiency of K173R.