Reflection High Energy Electron Diffraction (RHEED) is extensively utilized for characterizing crystal structures. Compared to X-ray diffraction, RHEED offers the advantages of simplicity in operation and strong diffraction signals, holding great potential for applications in university physics and solid-state physics education. However, the lack of mature and intuitive simulation methods for RHEED patterns has hindered its broader adoption in educational settings. This article begins with the free-electron plane wave model to discuss the theoretical model of RHEED and extends it to the case of finite-sized crystals, providing detailed mathematical exposition. The results of this model fit well with relevant experiments, demonstrating its effectiveness and promoting the application of RHEED in related teaching fields.