Digital holography has the advantages of high measurement accuracy and real time, and has high application value in many fields; photopolymer, as an optical storage medium, is one of the most promising holographic recording materials, but the thickness shrinkage caused by the photopolymerization reaction during the recording process greatly affects the recording effect, and in order to measure the specific shrinkage of its thickness, a digital holography-based measurement method for the shrinkage of photopolymer is proposed. The experimental system is designed based on the Mach-Zender interferometric optical path, and the holograms of the photopolymer before and after the reaction are recorded, and the phase change is calculated by using the holographic interferometry method.