Visible light sensitive polymer, Poly (4-dimethylamino-4'-(vinylbenzyloxy) benzalacetophenone) is effectively prepared by the condensation of Poly (4-vinylbenzyloxy) acetophenone with 4-dimethylaminobenzaldehyde in alkaline catalyst. Absorption spectrum of the condensation polymer shows the absorption maximum at 410 nm and the terminal wavelength at 520 nm, respectively. Poly (4-dimethylamino-4'-(vinylbenzyloxy) benzalacetophenone) film is coated on the aluminium plate, and crosslinked by the irradiation of visible-light. The sensitivity of the film is higher than the commercial PS plate, so that the photopolymer may be used by Ar ion laser and tangsten lamp irradiation in future. The photopolymer is applicated to lithographic plate, and good image is produced in lithographic proofing machine.