Abstract: Automatic reconstruction of building from DSM is presented.Focusing the ROI(regions of interest) is a pivotal step in reconstruction.The contour tracing is adopted here to get the ROI and every level of building's closed boundary is acquired simultaneously.The normal analysis of ROI is discussed to select the geometric model and reconstruct the roof.The closed boundaries are adjusted by least square refining to constitute the multi-orthogonal and multi-level buildings.The geometric models used are prismatic(flat roof) and parametric(gabled roof).