Abstract: A contact & stomach method was established. Using this method the toxicities of four insecticides, chlorpyrifos, phoxim, benfuracarb and imidacloprid to 3rd-instar larvae of Bradysia odoriphaga were determined. With phoxim as a standard insecticide,the relative toxicities of chlorpyrifos, imidacloprid and benfuracarb were 10.36,2.61 and 2.30, their field effect ratios were 9.58,1.88 and 2.05, respectively. The results showed that the accordance of the toxicity turn of 4 insecticides obtained by contact & stomach method in lab with the control effect turn obtained in field trial was better than that of contact method toxicity turn with field effect. The precision of contact & stomach method was also high. At last, the influence on toxicity of different treatment methods to larvae was compared and discussed.