Abstract: The resistance of methamidophos in N. lugens was selected in laboratory and the successive changes in carboxylesterase (CarE) and acetylcholinesterase (AChE) insensitivity were also analyzed. The results showed that the speed of methamidophos resistance development varied with generations. Resistance change was small before the fifth generation and after the fifteenth generation, and the change was sharp between the fifth and the fifteenth generations with one inflexion at ninth generation. The rise of CarE activity was very significantly correlated with the resistance change of F0~F16, with the correlative index 0.990 6. And AChE insensitivity (I50) from F8 to F16 also had the significant correlation with the resistance development, with the correlative index 0.970 1. Therefore, it was concluded that the increasing of CarE activity may play an important role in the resistance development and the AChE insensitivity also may play an important role at the late stage of the resistance development.