The invention provides a high-toughness photosensitive resin for 3D printing and a preparation method thereof. The photosensitive resin comprises a photosensitive resin (maleable photosensitive resin and rigid photosensitive resin), an active diluent, a light initiator and an additive. The method first synthesizes the toughness photosensitive resin (maleable polyurethane acrylate and epoxy modified polyurethane), and then the maleable photosensitive resin is mixed with the rigid photosensitive resin, active diluent, light initiator and additive. The maleable photosensitive resin is prepared from a polymer soft segment, which is a mixture of one or more selected from of polypropyleneoxide glycol ether, PTMG, hydroxyl-terminated polybutadiene, hydroxyl-terminated styrene butadiene rubber, hydroxyl-terminated butadiene acrylonitrile rubber and hydroxyl-terminated polysiloxane, and a polymer hard segment of toluene diisocyanate or isophorone diisocyanate, through hydroxyethyl acrylate or epoxypropanol termination. The photosensitive resin is applicable to DLP or SLA type 3D printers for modification of the existing 3D printing photosensitive resin, has excellent bending strength, and can directly print out elastic models.