The present invention relates to the technical field of medicine, and specifically relates to a PUMA inhibitor, a method for preparation thereof, and a use thereof. The PUMA inhibitor is the compound as shown in (I) or a pharmaceutically acceptable salt thereof. The definitions of its substituent groups are as described in the description. The compound (I) or pharmaceutically acceptable salt thereof is capable of targeting a PUMA protein and has very good physicochemical properties, very good apoptosis resistance and radiation protection effects; it can selectively inhibit the competitive combined effect of a PUMA protein and a Bcl-2 apoptosis-resistant protein, block apoptosis, and effectively protects against bone marrow damage. The present invention provides a new idea for, and powerful proof of, the application of a PUMA-protein small molecule inhibitor in radiation-protection pharmaceuticals, and is likely to become a highly effective, low-toxicity, and stable clinical radiation-protection pharmaceutical.