A high-precision three-dimensional (3D) imaging method using four-sided tower mirror scanning is proposed, herein, with the aim of solving the problems of low scanning efficiency and small angle of view of unmanned aerial vehicle (UAV) airborne lidar in the current 45° mirror scanning mode. First, a four-sided tower mirror structure for unmanned airborne LiDAR scanning was designed. Second, the scanning imaging model of this tower mirror was established, and its scanning coordinate equation was thus derived. Third, the track characteristics and influencing factors of the tower mirror were analyzed and compared with the scanning track of the 45° mirror. Finally, the qualities of the 3D laser point clouds obtained by the four-sided tower mirror and 45° mirror scanning UAV airborne laser radar were compared through experiments; the results indicate that the scanning efficiency of the former is more than three times that of the latter at the same speed. Additionally, the scanning point cloud has high density, small thickness, and good penetrability; it has broad application prospects in high-precision topographic mapping.