Abstract: A device for detecting a defect of a laser welding cover lens includes a coaxial light source configured to emit collimating detection light, wherein the direction of the detection light is perpendicular to a preset horizontal direction; a half transparent and half reflecting mirror arranged above the coaxial light source to reflect the detection light to a preset position; a reflecting mirror configured to reflect light from the half transparent and half reflecting mirror to the cover lens; an industrial camera parallel to the half transparent and half reflecting mirror and the reflecting mirror and configured to receive incident light from the detection light to obtain a detection image, wherein the incident light is reflected by the cover lens and passes through the reflecting mirror and the half transparent and half reflecting mirror; and a processor configured to determine whether there exists a bad point on the cover lens.