To analyze the effect of the system error on a large field of view infrared multispectral scanner, and provide the basis for determining calibration program, airborne infrared scanner imaging simulation was completed by using strict imaging model. For the un-coincidence of camera projection center and the rotation center of stable platform, the relationship between camera placement errors and POS system placement errors was focused on. Simulation results show that the effect of camera placement errors and POS system placement errors on the positioning accuracy are basically the same, there is a strong correlation between the two but it decreases with the sweep angle increases; when the sweep amplitude is less than 20°, the camera placement error can be incorporated into the POS system placement errors. This conclusion can provide reference for later calibration program design.