Abstract: An automatic hexahedral mesh generation algorithm for many-to-many sweep volumes is presented in this paper.By means of virtual decomposition,a many-to-many sweep volume is automatically decomposed into several many-to-one sweep sub-volumes.The sub-volumes are meshed by a previously proposed many-to-one sweep method,and the mesh for the many-to-many volume is generated by combining all of the sub-volume meshes.The virtual decomposition process for many-to-many sweep volume is the key for the success of the mesh generation algorithm,and this is focused in this study.Moreover,a novel procedure for imprinting target loops onto source loops is proposed to make them match in topology.The imprint procedures proposed in previous studies need discuss various cases to ensure robustness,thus suffer heavy coding efforts in practice.The new imprinting procedure is based on an enhanced boundary constrained Delaunay triangulation algorithm.It is conceptually simpler and contains no discussions on various cases that are essential to the previous procedures.Finally,two mesh examples and their quality data are presented to validate the efficiency and effectiveness of the proposed algorithm.