Abstract: The positioning accuracy of the positioning piece of welding tooling directly affects the quality of high-precision welding of automobile body-in-white, and the current positioning accuracy monitoring mainly adopts manual regular measurement mode, and there are problems such as high cost and low efficiency. Based on the linear measurement principle of laser beam, a low-cost online monitoring method of positioning accuracy of positioning block using point laser was proposed. Lasers and sensors are installed on both sides of the positioning piece, and the laser irradiates the positioning block so that the beam center hits the sensor on the other side after passing through the upper surface, and the sensor collects the light point data, extracts the edge position through filtering and binarization processing, realizes the measurement of the surface displacement on the positioning piece, so that the positioning accuracy of the positioning block is monitored in real time. The point lasers and sensors commonly used in this method belong to commercial off-the-shelf, do not need to be customized, have the advantages of low cost, high reliability, etc., and have strong engineering practicability. Experimental results show that the proposed method can control the positioning accuracy error within 0.02mm, which meets the requirements of high-precision welding.