Abstract: The infrared (IR) characteristic of a turbofan engine exhaust system with lobed mixer was studied experimentally and numerically, and the results were compared with a relevant annular mixer exhaust system. The results show that, the lobed mixer can enhance the mixture of core flow and fan flow and reduce the plume temperature, making the plume IR radiation attenuated; compared with the annular mixer exhaust system, the IR radiation intensity of the lobed mixer exhaust system reduces at least 9% in the direction right behind the nozzle exit, and reduces more than 39% in the direction vertical to the axis of the nozzle exit; the axisymmetric nozzle with low emissivity and high reflectivity has negative effect on IR suppression because of its strong reflection to the radiation of the high temperature components within angles range from 40 to 70, thus, it is appropriate to increase emissivity and reduce the reflectivity of nozzle wall in order to achieve better IR suppression.