The invention discloses polyurethane-modified flexible epoxy acrylic resin, a preparation method of the polyurethane-modified flexible epoxy acrylic resin, photo-curing identification oil ink and a flexible printed circuit board. The preparation method of the polyurethane-modified flexible epoxy acrylic resin comprises the following steps: firstly, preparing a semi-addition product of diisocyanateand acrylate-hydroxy ester and flexible epoxy acrylic resin; then performing reaction on the semi-addition product of diisocyanate and acrylate-hydroxy ester and the flexible epoxy acrylic resin to obtain the polyurethane-modified flexible epoxy acrylic resin. The polyurethane-modified flexible epoxy acrylic resin is prepared by adopting the method, and the photo-curing identification oil ink isprepared from the components in parts by weight: 30 to 50 parts of polyurethane-modified flexible epoxy acrylic resin, 1 to 5 parts of photoinitiator, 10 to 30 parts of active diluting agent, and 15 to 40 parts of filler; the flexible printed circuit board comprises a circuit board body and an identification part adhered to the circuit board body, and the identification part is formed by curing the ultraviolet photo-curing identification oil ink.