A method based on annular laser vision sensing for automatically locating the welded seam includes such steps as detecting annular laser tracings by CCD planar array, imaging on image sensing surface of camera, obtaining the expression equations for the X and Y coordinates of the characteristic points of said welded seam in conic coordinate system of laser, finding out the depth value of said characteristic point according to circular radius-depth relation algorithm, creating the equation for the Z coordinate of the characteristic point to be detected, finding it out, and converting the found out 3D coordinates from said conic coordinate system to the coordinate system of robot itself. Its advantage is high efficiency.