The simplified radiance model of midcourse ballistic target, and the infrared focal plane model based on point spread function and target tail, were presented. Integrating the calculations for target space position and the position in 2D focal plane projected from 3D space, the imaging of midcourse ballistic object target complex in space-based infrared sensor were simulated. With the analyses to the simulation results, it is confirmed that the midcourse ballistic object target complex gives rise to new challenges for detection and tracking techniques of space-based infrared sensor. The methods meeting these challenges were afforded.