The selection of detection band is fundamental to the design of infrared warning satellites. An approach adopting point target radiation flux apparent contrast spectrum to select the detection band was proposed in this paper. A relatively complete model calculating the apparent contrast spectrum of rocket plume was founded at first. Then the infrared radiation spectral characteristics of typical liquid and solid rockets at various altitudes were obtained by modeling and simulating. Finally, the infrared radiation of background and the transmittances and path radiation of atmosphere were calculated using the combined atmospheric radiative transfer(CART). Based on the above results, the apparent contrasts spectral of typical liquid and solid rockets at various altitudes were gained. Results of both liquid and solid rockets show that, the apparent contrast at 2.55～2.85μm and 4.19～4.48μm are higher than other bands, and might be suitable for the infrared warning satellites detection band chosen by the space based infrared system.