In order to realize calibration of the camera carried by the ins pection robot on site and obtain the intrinsic parameters such as the focal length,an automatic calibration method is proposed based on the Zhang′s algorithm.In the method,the ground wire and moving objects on it are detected by vision method,an d then the robot is controlled to move slowly along the wire when the object is found.When the object enters processing area,the fro nt point coordinates of the object are recorded,and then two angles of view are transformed to obtain a series of images from three viewing angles.In image processing,the front points on the object in n images from each visual angle spaced at Δn frames are extracted,and then a checkerboard with 2×(n－1) grids is formed at the intersection point of the vertical line through the points and the axis l ine and the two sides of the ground wire.Then,by using the known conditions such as the size of the wire,the speed of the robot and the ti me difference between the processed frames,the relation between the grid points in the image and its three-dimensional space points are obtained.Finally,the intrinsic and extrinsic parameters of the camera are calculated by the same processing method of Zhang′s calibrati on method.It is proved by experiment that the error of the focal length is less than 5% in terms of Zhang′s calibration resul ts.The automatic calibration during the work of the camera can be realized in the method,and manual calibration model is not need,so the whole work can be done by machine.