The basis of using 3D LiDAR in engineering application is to calibrate the external parameters of LiDAR, and the external parameters of LiDAR usually need to calibrate the data of other sensors jointly, and the calibration method is complicated and the process is long.In this paper, a simple automatic calibration algorithm is proposed.The algorithm first uses RANSAC algorithm to draw up a number of planes, and through the angle of the normal vector of the adjacent points for the secondary screening plane equation, then according to the plane equation to get the coordinates of the intersection point between the planes, using the antisymmetric matrix to construct the rotation matrix, further using the intersection point coordinates in the radar coordinate system and the world coordinate system under the difference, to obtain the approximate transformation relationship.Finally, the approximation matrix is optimized by the least square method, and a more accurate rotation displacement matrix is obtained.In the absence of feature points and corner clouds, the proposed algorithm can be used to fit more accurate corner points by plane equation. The simulation results show that the proposed calibration algorithm is feasible.