Regarding the deficiency of traditional deformation monitoring in effectively detailing deformation of local unique monitoring objects due to the overall deformation model, this paper proposes a three-layer mixed deformation model, i.e., block, region, and overall deformation, based on terrestrial 3D laser scanning technology. A block-based deformation calculation method is also designed. This method mainly includes object segmentation, deformation estimation, and deformation fusion, and can automatically extract deformation information of different scales without prior monitoring information. Simulation results show that under this method, the mean angle change estimation error of RANSAC algorithm plane fitting regression is 1.21″, and the estimation reliability increases with an increase in block size within a certain range. The results of the landslide experiment show that the minimum value method has less displacement estimation noise, and a 0.2 m block size segmentation can provide further deformation estimation details. The proposed method is particularly suitable for monitoring fields with nonuniform deformation characteristics, and has certain theoretical and practical significance for promoting the transformation of disaster monitoring from"point monitoring"to"surface monitoring"for landslides and other disasters that are difficult for personnel to reach.