Abstract: Geometric and numerical simulation models of a forced lobe mixing exhaust system with different lobe numbers were created.Though three-dimensional numerical simulation,the principle of effect of different lobe numbers in a forced mixing exhaust system was obtained.The results show that,non-dimensional average streamwise vorticities increase at the trailing edge of the lobe mixer with the growing number of lobe.At the exit section of the forced mixing exhaust system,thermal mixing efficiency declines as the lobe number increases;and the total-pressure recovery coefficient firstly increases when the lobe number increases from 8 to 16,then declines when it augments from 16 to 20 and finally increases when it rises from 20 to 24.