The circulator is a commonly used element in the microwave system, which is capable of selecting the directional propagation of microwaves. Since the microwave element is different from a low frequency centralized parameter element, the students are not easy to form a clear physical image. In this paper, the model of ferrite circulator is established by using COMSOL software. The influence of geometric parameters on the directional guided wave performance of circulator is quantitatively studied by using scattering matrix element (S parameter), and the corresponding geometric parameters when the performance is better are determined; The propagation behavior of microwave in the circulator is intuitively displayed by electric field distribution diagram and energy flow direction diagram. It is very helpful for students to establish the physical image of directional transmission of microwave by circulator.