This paper explores the inhibitory effects of three insecticides, losban, fenpermethrin, dichlorvos, and their combinations on esterase of Tetranychus cinnabarinus in vitro. The inhibitory concentrations of these three insecticides were 2.8128×10-6, 3.1698×10-6, 4.1586×10-6 (mol/L), respectively. The results indicated that the inhibition of tetranyl on tetranyl esterase was the strongest, followed by fenpermethrin and dichlorvos. By measuring the Mi constant and the maximum reaction speed of insecticide on tetrasarinase cinnabarinase, it was found that the action mode of losban and fenpermethrin was competitive inhibition, and that of dichlorvos was non-competitive inhibition. The combined inhibitory effects of dichlorvos + levos and dichlorvos + fenpermethrin were additive, and the combined inhibitory effects of levos + fenpermethrin were synergistic and competitive.