In order to improve the accuracy of the flash intensity test system of the flash light bang, two models including an error calibration model and a single-element regression modification model were used to compensate the coaxial error. Original detection accuracy has been increased from 10E-6 to 10E-7 and the system accuracy has been increased from 10% to 4% by this method. So the system-test accuracy of the flash intensity of the flash light bang has been highly increased. This research is a step in the direction that to improve the test accuracy of the flash light bang's intensity.