Abstract: Due to the cost limitation of industrial application, the quality nondestructive testing technology of medium and small shield tunnel has a serious loss of accuracy and speed when it is transferred to the large-diameter shield tunnel. A large-shield tunnel forming quality inspection vehicle is developed with the rail inspection vehicle as the carrier and integrated with two-dimensional laser scanner, encoder and computer equipment. An asymmetric shield quality inspection method based on digital image is proposed. By analyzing the construction environment of large-diameter shield, the ground and vehicle body point clouds are filtered out, and the central axis is extracted by neighborhood vector method, and the central coordinate system of tunnel is established. The sampling point cloud was divided into dense side and sparse side point cloud according to the sampling distance. Different methods were used to pick up the joint features of the segment. The dense side point cloud was expanded around the central axis into two-dimensional gray image, and the joint image was segmented by scaling, normalization and gradient threshold segmentation. According to the classification of joints based on the linear equation, the linear distribution formula of sparse side joints and dense side joints was deduced by combining with the segment structure and the point placement, and the sparse side joints were picked up indirectly. According to the joint characteristic points, the edge point clusters on both sides of the segment were calculated, and the segment misalignment was calculated. The least square method was used to fit the tunnel point cloud and calculate the tunnel ellipticity. In order to verify the effectiveness of the inspection method, inspection tests were carried out in a large-diameter shield tunnel, and the test results showed that: The inspection speed of the molding quality inspection vehicle in the 14-meter shield tunnel is 3km/h, and the error detection deviation is less than 2mm and the ovality detection deviation is less than 1‰ compared with the traditional method, which can meet the requirements of high speed, high precision and low cost of large-diameter shield tunnel molding quality inspection.