To address the problem that the point cloud on the bottom surface of the measured object cannot be acquired efficiently in 3D laser inspection, a supplementary perspective 3D point cloud scanning method based on the principle of right-angle prism refraction is proposed in this paper. The method adopts a right-angle prism to refract the bottom view image to the side, compensating for the lack of a bottom detection viewpoint for 3D detection and complements the bottom detection viewpoint. The sealing ring is taken as the defect detection object, and a structured light 3D camera is employed to collect the 3D point cloud. Compared with the direct scanning methods, this approach allows for real-time and rapid identification of surface defects with intact sealing rings in a single operation. It particularly simplifies the detection of bottom defects, eliminating the need for specialized gripping devices or complex mechanical structures such as robotic arms, and only the addition of a right-angle prism is required. Experimental results demonstrate that the point cloud scanning method with the supplementary perspective using a right-angle prism can meet the imaging requirements and effectively detect common defects such as fracture and collapse in sealing rings, achieving a detection accuracy of 100% and fulfilling the requirements of sealing rubber ring defect detection.