Abstract: The equipment of visible light backlit shadowgraph was built, and 0.7-4.6 μm resolution corresponding to 4-30 cm measured distance was acquired. The target in sample room could be accurately fixed within 0.1 mm. A backlit shadowgraph technique was developed. The different resolution shadowgraphs of plastic and glass targets were gained using this technique. The precise measurement and calculation method were built for studying DD/DT ice thickness by gaining the ray energy density image and ray trace model of target. The research detection using shadowgraph and ray interfere technique together could obtain a method of nondestructive measure refractive index of plastic targets. The result shows that the backlit shadowgraph is valid for diagnosing transparent cryogenic target parameter.