This study applies terrestrial laser scanning technology for data measurement in brick-concrete structures, using wall length as the primary index to monitor deformation. Firstly, after determining the two distance thresholds based on thickness, the single wall point cloud is acquired by building point cloud segmentation and wall point cloud redistribution. Secondly, using the single wall as the fundamental unit, the wall boundary points are estimated. This estimation method is changed from the point cloud boundary estimation method based on normal. It only needs to calculate the normal once and convert the coordinate system once. Thirdly, with the constraint that two adjacent top boundary lines intersect at a point, the top boundary line is fitted by the weighted iterative least squares method. Fourthly, for single wall, a downward-translatable interest region is created and the structural length in the region is calculated. Finally, for two consecutive measurements, the wall lengths obtained of the same translations times are difference to extract the deformation values. The results show that the deformation discerned from the wall length calculated through this method aligns with the deformation represented by wall fractures. Furthermore, the computational error associated with the wall length ranges between -3 mm and 7 mm, thereby attaining millimeter level precision.