Head-up Display (HUD) is a large aperture optical system with a large view field. Head-moving is the usual measurement, but has a low accuracy, and relying on the subjective judgment of the inspector. In order to improve the testing accuracy and efficiency of head-up display’s optical parallax, and avoid the subjective judgment of the inspector, an optical parallax auto-testing system was introduced. The image of head-up display was collected by the CCD camera, and then the camera moved in the out aperture. The difference was calculated by comparing the image collected at the edge of the out aperture, and then the head-up display’s optical parallax was obtained. The testing principle was introduced in detail, and the structure of the optical parallax testing instrument was introduced in detail. Then the parameters and testing accuracy were also analyzed. At last, the testing accuracy of optical parallax was analyzed in several.