The invention discloses a laser welding abutted seam measuring system based on a plano-convex cylindrical lens. The system comprises a light source, the plano-convex cylindrical lens, a convex lens, a photosensitive element and a data acquisition unit, wherein the light source is used for emitting detection light irradiating an abutted seam to form reflection. Optical axes of the plano-convex cylindrical lens, the convex lens and the photosensitive element are overlapped, the optical center line of the optical axes and the light source and the direction vector of the abutted seam are positioned in the same plane, reflected light sequentially passes the plano-convex cylindrical lens and the convex lens along the optical axes after the detection light irradiating the welding abutted seam is reflected, finally, images are formed on the photosensitive element and acquired by the data acquisition unit, and measuring results reflecting characteristics of the abutted seam are correspondingly obtained. The invention further discloses a corresponding measuring method. Geometric details can be amplified and reserved in the width direction of the abutted seam, a wide image acquisition range is obtained in the length direction of the abutted seam, and accordingly, the laser welding abutted seam can be precisely measured.