Aimed at studying the influence of flight parameters on the infrared radiation of a liquid rocket exhaust plume, the FLUENT software is used to calculate the flow field of an exhaust plume under several different flight parameters, then the HITEMP database is adopted to calculate the radiation parameters and the finite volume method (FVM) is used to calculate the infrared radiation between 2 μm and 5 μm. Based on this work, the influences of the altitude and velocity on the spectral radiation intensity as well as 2.5~3.0 μm and 4.2~4.7 μm band radiation intensity are studied. It is found that, the influences of flight parameters on the infrared radiation are exerted by changing the temperature and size of the exhaust plume flow field. At the same velocity, as the altitude increases from 0 to 40 km, the infrared radiation intensities increase gradually, and the band radiation of 4.2~4.7 μm increases faster. At the same altitude, as the Mach number increases, the infrared radiation intensity decreases at first and then becomes stable, and the band radiation of 2.5~3.0 μm decreases faster.