Microstructure plays a significant role in the evolution of short fatigue cracks. The modelling procedure of microstructure for polycrystalline materials is presented in this paper. The factors that effect on the modelling of microstructure are discussed in detail. Firstly, the 2D microstructure of LZ 50 steel with straight grain boundary is simulated with the help of Voronoi tessellation. To validate the modelling results of the microstructure, two load cases are intentionally designed to verify the microstructure for the view of comparing the results with homogeneous material under the same load cases. The whole process is carried out with the application of FEM. From the comparison of mechanical properties generated by the simulated microstructure with anisotropic material property to the ones showed by macrostructure with homogeneous material property, the validity and convenience of the modelling process is shown. The simulated microstructure for polycrystalline materials can be used for the further research on the initiation and growth of short fatigue cracks.