Abstract: ObjectiveBy comparing the sensitivity and activity of Acetylcholinesterase and Carboxylesterases to DDVP between sensitive strain and resistanthouse fly,a linear relationship among the level of DDVP-resistance,DDVP-sensitivity to Acetyl-cholinesterase and the level of DDVP-control to Carboxylesterases,and a non linear relationship among the level of DDVP-resistance,the activity of Acetylcholinesterase and Carboxylesterases were found.MethodsThe DDVP-sensitivity of Acetylcholinesterase was used as the biochemical label of house fly resistance.The frequency and change among seasons of nonAcetylcholinesterase sensitive strains of house fly were detected among 4 districts in Beijing.ResultsThe frequency of nonAcetylcholinesterase sensitive strains of house fly in Fengtai district is significantly higher than the other 3 districts until October.The frequency of non-Acetylcholinesterase sensitive strains in Haidian district is the lowest and the level of changes is distinctively lower than that in Fengtai.The strains of house fly in Xicheng district are similar to Haidian and the strains in Chaoyang are similar to Fengtai.ConclusionIt is possible to use chemicals to controt Car E and AchE sensitivity as the biochemical label of resistanthouse fly to detect the change of house fly resistance.