Abstract: The resistance level of field populations of diamondback moth collected from 3 different regions of Yunnan province was determined using leaf-dipping method and a susceptible strain maintained in the laboratory was used as control.The results indicated that different populations had different resistance levels to the insecticides.The resistance level to organophosphate insecticides varied from 1.74 to 31.1 times,to pyrethroid insecticides varied from 7.41 to 764 times and to avermectin insecticides varied from 5.60 to 4.06×104 times.In vitro and in vivo AChE inhibition experiments with inhibitors of dichlorvos and methomyl showed that there were significant differences in I50 (dosage of inhibiting 50% AChE activity) and IT50 (time for inhibiting 50% AChE activity) between Tonghai resistant and laboratory susceptible strain.In in vivo inhibition,the AChE I50 of Tonghai strain to dichlorvos and methomyl were 2.21 and 2.16 times higher than that of the susceptible strain,while in in vitro inhibition,the inhibiton were up to 209 and 26.5 times,respectively.The IT50 of dichlorvos to AChE of Tonghai strain under in vitro and in vivo inhibition were 0.32 and 0.17 times as much as that of susceptible strains,respectively,while for methomyl,the inhibition increased to 1.37 and 1.74 times.