Abstract: Objective In finite element analysis of microstructures, the rationality of the microstructure finite element model is one of the key factors. Currently, traditional Voronoi diagram methods struggle to accurately model characteristic structural units, such as weld columnar grains, equiaxed grains, and grain boundaries. Methods This paper improves upon the Voronoi diagram method. An elliptical region segmentation algorithm is employed to construct characteristic structural units of weld structure, and an intersection algorithm is applied to generate the set of grain boundary models, ultimately forming a finite element mesh model for weld microstructures. Results Comparisons between metallographic images and structure results based on structure simulation demonstrate that the microstructure grain boundary model established by the proposed method achieves high similarity to real structures, showing significant advantages over traditional Voronoi methods. The model is applied to coordinate grain-grain boundary strength constitutive modeling, yielding favorable results. Conclusion This paper innovates structure modeling methods, laying a foundation for future finite element analyses that distinguish between grain and grain boundary models.