Abstract: This paper reviews some current research on appearance-preserving simplification methods,and puts forward the multiple-step algorithm based on the hierarchical qua-tree expression of height-field model.First,the input model is simplified according to the physical attribute,and second,the stored result is further modified according to the appearance attribute.So,as the appearance attribute changes with interactive operation,run-time computation only involves the appearance modification with the assumption that physical attribute is still the same.Examples reveal that this multiple-step method is effective and robust for real-time simplification of height-field model.