For indoor environments, laser scanners cannot receive satellite signals, and engineering needs to obtain indoor point cloud coordinates. This paper proposes a back sight directional registration method: sweep the scanning site at a known point, scatter the target site at another known point, and accurately scan the target to obtain the precise feature points of the back-sight point. The data of the scan site are converted to a known point coordinate system during data processing. Experimental results show: the method can not only register the two-site cloud data with high precision, but also have higher precision of the point cloud coordinates after converting the coordinates. To meet the actual engineering needs, it can provide reference for engineering applications such as indoor scanning and tunnel scanning.