Abstract: It has been the focus of the study for effective detection of low altitude penetration target which has low altitude, short flight time. To 2.7 m, 4.3 m wavelength as the center of the detection system, a near space infrared detection image plane irradiance model was established. SBIRS space-based infrared system and the near space detection system were simulated. Simulating typical target trajectory, considering the atmospheric effects, infrared radiation image plane irradiance and modulation contrast of object and background of boost phase and post-boost phase at SBIRS and near space platform were obtained. Simulation results show that near space platform has a higher signal contrast and a longer detection time than SBIRS. For TBM's post-boost phase, the detection effect of 4.3 m is better than that of 2.7 m as detection center wavelength.