Conventional surveying method could not solve the problem of detecting building's whole deformation in a short time, including in particular flatness and inclination values of the surface of the building. Aiming at this problem, this paper introduce a method to solve it based on terrestrial laser point cloud, first step is fitting point-cloud datum to point-cloud model for reducing random errors in original point cloud, and then calculating the distance between original points to fitting model on homogeneous region and upon determining root mean square error about this distance as a flatness i...