Abstract: Building with parallel structures is the most popular kind in modern city.As the widely used 3D city model,more and more generalization methods for this kind of building have been developed.This paper begins with the structuring of 3D building data and then a data structure that benefits the generalization is proposed.Orthogonal of building,introduction of polygon and acquisition of feature information are used in building construction.According to the requirement of visualizations,LODs of city buildings are divided into three levels.Based on which,a simplification algorithm of shifting facet based on minimal distance is realized in the simplification of the building with parallel structures.Experiment was done to prove the good efficiency and usability of the algorithm and the algorithm works well in simplification of buildings with parallel structures.