The invention belongs to the field of resin synthesis, and relates to an ultraviolet-curing phosphate ester modified acrylic resin and a preparation method thereof. The method concretely comprises the following steps: mixing monohydroxy acrylate, hydroxy acrylic resin, a polymerization inhibitor and an organic solvent, stirring and heating above materials to 45-50DEG C, slowly and uniformly adding phosphorus pentoxide while stirring, stirring and heating all above materials to 70-90DEG C, carrying out a reaction for 3h until a detection result shows that the pH value is basically stable, adding an acrylate active diluent accounting for 30-60% of the total mass of all above materials, carrying out heating and pressure reduction distillation to remove the organic solvent in order to obtain the acrylate active diluent diluted ultraviolet-curing phosphate ester modified acrylic resin. The acrylic phosphate modified acrylic resin prepared through grafting the acrylic resin with acrylic phosphate integrates the low shrinkage of the acrylic resin with the adhesion promotion of a phosphate group. The ultraviolet-curing phosphate ester modified acrylic resin can be used as a main body resin for difficult-adhesion substrates, and has excellent adhesion.