Abstract: A vehicle-mounted lidar external parameter joint calibration method and system, a medium and a device. Said calibration method comprises: respectively acquiring point cloud data of the reference radar and point cloud data of a radar to be calibrated, obtain a corresponding plane A point cloud and a corresponding plane B point cloud, and calibrating a rotation matrix; rotating the plane A point cloud corresponding to said radar by means of the rotation matrix, and obtaining a z component of a translation matrix on the basis of the rotated plane A point cloud and the plane A point cloud corresponding to the reference radar; and obtaining a calibration column point cloud from the point cloud data of the reference radar, and obtaining x and y components of the translation matrix on the basis of the calibration column point cloud and the rotated plane A point cloud corresponding to said radar.