To accomplish interactive visualization and real-time rendering in 3D cyber city, Level of Detail (LOD) technique can generate different details of data sets according to viewing parameters and application requirements to reduce computation. This paper proposes a semi-automatic approach for the generalization of 3D polyhedral building models to formulate LOD representations of complicated buildings for high performance visualization of cyber city. The idea is to apply generalization in two dimensional (2D) orthographic views of 3D buildings and reconstruct the simplified 3D models accordingly. Building models with non-planar roofs or special structures are further processes with developed semi-automatic algorithms. Experimental results demonstrate that the proposed method is effective in generalizing most planar 3D building models. For 3D building models with non-planar roof structures and curved elements, the proposed method can also generate multiple LODs of the models while preserving important visual characteristics of complicated buildings.