In order to solve the problem of long range detection and discrimination of the anti-tactical ballistic missile (TBM), this paper proposes an operational concept that the targets will be detected based on the coordination the near space platform with radar. The Characteristics of the near space and the attenuation of IR transmission by space atmosphere are analyzed qualitatively. Taking the platform altitude, telluric curvature, atmosphere IR transmission characteristic and so on into account, the near space atmospheric transmittance model of IR transfer is set up. On the basis of above, the IR model of Midcourse TBM Based on Near Space Detection is designed. Finally, the model is simulated mathematically with MATLAB. The simulation results verify the effectiveness of near space atmospheric transmittance model and simultaneously indicate that the IR detecting ability of the TBM is very strong for the near space platform in given altitude.