The embodiment of the invention provides a multiple-cavity ejector for continuously spraying a coiled material, comprising a uniformly mixing cavity, a middle cavity and a flat nozzle, wherein the uniformly mixing cavity is communicated with the middle cavity; the flat nozzle is the outlet end of the middle cavity; and the uniformly mixing cavity is provided with a powder supplying joint used forsupplying powder paint to the uniformly mixing cavity and an air supplying joint used for supplying compressed air to the uniformly mixing cavity. The embodiment of the invention can realize the uniform powder spraying in the width direction of a sprayed base material and is suitable for the spraying production of the high-speed coiled material; and in addition, the multiple-cavity ejector has the advantages of simple structure, easiness of processing and manufacture, convenience of operation and maintenance and very low investment and using cost.