Abstract: In this paper we propose a manifold-guaranteed out-of-core simplification algorithm based on vertex clustering,referred to as MAG-Simp.All the manifold parts generated by vertex-clustering strategy are categorized into three types,triangle segments,inherent non-manifold edges and inherent non-manifold vertices.All the three types of non-manifold parts can be converted into manifold by simple operations.Our MAG-Simp algorithm does not require the input with manifold topology while the manifold topology of the resultant models could be guaranteed.Both the efficiency and simplicity of vertex clustering strategy and the quality of the simplified model are maintained.