Abstract: The systemic activity of 7 neonicotinoid insecticides in leeks and its toxicity against the 4th instar larvae of Bradysia sarcophaga (Diptera: Sciaridae) were studied and compared by hydroponic method under different cultivated conditions. The results showed that with the prolonging of the hydroponic time, the toxicities of the 7 insecticides inside the leek against the larvae were all enhanced. Under concentration of 100 mg/L, the generation of the systemic toxicity of clothianidin and imidacloprid was faster than that of the other neonicotinoid insecticides, causing mortalities of the 4th instar larvae 32.38% and 36.50% at 72 h, respectively; The mortality of dinotefuran reached the highest, which was 96.35% at 168 h. When treated by the same concentration of one insecticide, the generation of lethal activity in leek foliage was faster and the mortality was higher than that of the stem. The higher the cultivated temperature and solution concentration tested, the faster the generation of toxicity and the higher the mortality showed. The results of present study indicated neonicotinoid insecticides could be used to control the chewing mouthparts larvae of B. odoriphaga in leeks through root treatment.