When an IR CCD (Infrared Charge Coupled Device) is directly illuminated by the sun or works for a long time, the thermal halo background in the infrared image sequences can be observed. The luminance and contrast of the image obtained by the IR CCD are generally low, so the influence of the thermal halo background on the IR image is serious. In order to eliminate the influence of the thermal halo, a method of real-time IR image background compensation by using the digital image processing means - subtraction, reversed addition is submitted. Then, a hardware designed on the basis of those methods is used to implement in the FPGA (field programmable gate array) in real time. The experimental result has indicated that the image's quality can be improved by the thermal halo background compensation.