Aimed at studying the influence of afterburning on the infrared radiation of a solid rocket exhaust plume, a model which can calculate the afterburning flow field and infrared radiation of a solid rocket exhaust plume is founded. The Fluent software is used to calculate the afterburning flow field of a solid rocket exhaust plume. Then, a narrow band model and the Mie scattering theory are employed to calculate the radiation parameters of gas and Al2O3. The finite volume method (FVM) is used to solve the radiation transfer equation (RTE). Based on this model, the influences of afterburning on the infrared radiation of solid rocket exhaust plumes both without and with Al2O3 are studied respectively, and the cause of the difference of the influence degree between the two cases is analyzed. Results show that, afterburning can enhance the infrared spectral radiation of the plume without Al2O3 greatly, and the average increase radio of the two domain radiation band of 2.5～3.0 μm and 4.2～4.7 μm achieve 46.4% and 58.4% respectively. Besides, the radiation increment of plume with Al2O3 is smaller, and the average increase proportions of the two radiation bands 2.5～3.0 μm and 4.2～4.7 μm achieve 7.7% and 8.4% respectively. It is considered that the difference of infrared radiation increment results from the difference of temperate increment between the two cases.