Abstract: An experimental study on the lobed nozzle of an infrared suppression system has been carried out at the low-speed wind tunnel with the electrical heater.The total temperature distribution at mixing flow exit and the temperature distribution on mixing duct and sheltering sheath were measured under different mass flow ratios of secondary stream to primary stream and differeat distances of the mixing duct from the sheltering sheath.The results show that ambient air mixing plays a dual role for reducing the exhaust temperature and mixing duct temperature.Sheltering from the hot wall makes the sheltering sheath temperature close to ambient temperature in case of the sheltering distance greater than 20 mm.Simultaneously,the plume irradiance and total radiation intensity for a typical lobed nozzle of an infrared suppression system were also measured to evaluate the infrared suppression effect.The data indicate that it does significantly reduce infrared radiation signature.