Purpose - In the finite element analysis of a hot forging process with hexahedral elements, flash region is difficult to analyze because of the thin shape. In this paper, a hot forging process is effectively analyzed by constructing a locally fine mesh in the flash region. Design/methodology/approach - When remeshing is decided by an error estimation and flash is generated, the boundary patch of the mesh is constructed and expanded in the normal direction of the flash region. After hexahedral mesh is constructed in the expanded patch with master grid approach, the boundary patch is compressed to the original shape and the nodes in the boundary are moved to the relative position of the boundary patch. Then, a locally fine mesh is constructed in the flash region. The quality of mesh on the boundary is again improved by adding surface element layer. Therefore, the hot forging process can be effectively analyzed by constructing the adaptive hexahedral mesh in the flash region. Findings - The results show that the locally fine mesh can be constructed in the hexahedral mesh generation procedure by constructing mesh in the expanded patch and compressing the mesh according to the original boundary patch without affecting the compatibility of element. Then, it is applied to the analysis of a hot forging process and it has been shown that the analysis result of the proposed technique can save the analysis time remarkably relative to that of the fine mesh, while maintaining the analysis accuracy of the fine mesh. Originality/value - In the finite element analysis of a hot forging process, the flash region is very difficult to analyze because it is difficult to construct locally fine mesh with hexahedral elements. A new adaptive mesh generation technique using hexahedral elements is suggested to overcome such difficulty and applied to the analysis of a hot forging process.