3D printed concrete has emerged as one of the most hotly researched 3D printing technologies due to its advantages of shaping without molds and intelligent construction. Given its low heat of hydration and low carbon emissions slag-based cement is becoming more widely used for 3D printing concrete. However, in the formwork-free shaping process, freshly printed slag-based concrete is immediately exposed to air and loses moisture much earlier than traditional cast-in-formwork concrete. As a result, there is a greater risk of drying shrinkage and cracking and poor volumetric stability of the printed part. This study investigated applicability of photo-polymerization technology in improving the volumetric stability of 3D printed concrete by using UV-curable polyurethane-acrylate (PUA) resin as in-situ sprayed coating on the surface of freshly printed slag-based cement samples. The results show that, in comparison with the uncoated 3D printed cement samples, the volumetric shrinkage of the coated 3D printed cement samples significantly reduced by 44 % after 28 days of environmental curing. For samples of the same age, the compressive strength of the coated test block was increased by 27 % from 20.03 MPa to 25.49 MPa, and the interlayer bond strength was increased by 41 % from 1.46 MPa to 2.06 MPa. The sprayed UV-curable polyurethane-acrylate resin can cure rapidly on the specimen surface within seconds under the irradiation of UV light to form an in-situ protective coating, which is tightly bonded to the surface of the cement, effectively reducing water dissipation and promoting hydration, allowing more even and condense microstructures to form during hydration from the outer surface to the inner part of the printed sample, resulted in a higher strength.