In alkaline medium, hydrogen peroxide oxidizes luminol and then produces chemiluminescence. Dimethoate could enhance the chemiluminescence intensity strongly, and thus a quick and direct flow injection chemiluminescence method based on luminol-hydrogen peroxide system was established to determine the content of dimethoate. The results indicated that the dimethoate concentration had a good linear correlation with chemiluminescence within the scope of 0.01 to 10mg/L. The detection limit of the method was 0.009mg/L. The relative standard deviation was 2.1% for eleven replicate detections of 0.5mg/L dimethoate. Using this system, the cauliflower samples were spiked with dimethoate and detected by this method with recovery ranging from 86.7%~109.5%.