Abstract: For the low contrast target acquisition test of the electro-optical equipment, a new method is proposed by using a contrast adjustable infinite distance target. The design of a contrast gradient adjustable optics infinite distance target device is introduced. This equipment may simulate the sky background luminance and a weak target in this background. It uses two integration spheres to simulate the background and target brightness independently. The collimating lens is installed in background integration sphere, target and its background become an infinite source. There were inner and outer light sources for integration sphere illumination. In the outer light source, a collimator was installed. It made parallel beam incident into the integration sphere. The size of the incident parallel beam was controlled by using diaphragm adjusting lever. This method didnt change color temperature, but luminance could be different. So background and target luminance became continuously adjustable under color temperature unchanged. The target contrast could change continuously, the range of variation is 0～90%, the contrast stability is better than 1%, the biggest background luminance exceeds 60W/m2sr.