Abstract: To screen out the combination of insecticide complex agents with synergistic effect on the underground pest Pleonomus canaliculatus, the toxicant force of each compound combination on the 3rd instar larvae of the Pleonomus canaliculatus was determined by the dipping method. The co-toxicity factor method was used to select the combination with the co-toxic factor greater than 20, and then the ratio was further refined, and the optimal compounding combination with a co-toxicity coefficient greater than 120 was screened by the co-toxicity coefficient method, among them, 28 groups had synergistic effect. The results showed that: chlorantraniliprole with chlorpyrifos, fipronil, thiodicarb, clothianidin, bifenthrin, thiame-thoxam and lambdacyhalothrin, with the ratio of 2:1, 3:1, 15:8, 15:2, 3:4, 1:2 and 3:11, respectively, showed significant synergistic effect, and the co-toxicity coefficient (CTC) was 178.41, 185.44, 208.10, 155.16, 149.55, 138.98 and 309.22, respectively; the most significant effect was observed when the mixture of lambda-cyhalo-thrin and thiamethoxam was at a ratio of 11:2, and the co- toxicity coefficient (CTC) was 198.45. The effect of bifenthrin combined with thiodicarb and clothianidin at a ratio of 1:2 and 1:5 is significant with the co-toxicity coefficient (CTC) of 215.69 and 337.94, respectively.