In the process of drying heavy wall workpieces and castings in powder coating production line,the cooling effect of conventional nozzle structure with strong cooling chamber is not ideal,and the cooling effect of workpieces themselves is poor.According to this situation,the structure of the strong cooling chamber was optimized,the structure of air duct through the strong cooling chamber was adopted,this structure can quickly take away a lot of heat on the surface of the workpiece,improve the heat exchange efficiency,and the required air volume is smaller than the conventional nozzle type strong cooling chamber,with remarkable energy-saving effect.