In this paper, a C-band strip-line circulator operating at 3 to 4.2 GHz is designed. The parameters of the circulator are designed and simulated by ANSYS High-Frequency Electromagnetic Simulation (HFSS) software. Isolation is one of the key indicators of the circulator's performance. The simulation results show that an isolation of the circulator in the mid-band range of 3.3-3.8 GHz is greater than 22 dB, and the relative bandwidth exceeds 14, which is sufficient for 5G spectrum n78. In addition, the return loss when port 1 excited is greater than 20 dB in the working frequency band. The relationship between uniform and non-uniform biasing simulations, ferrite and dielectric material selection are the main important point to considered for designing high isolation circulator. Therefore, the circulator presented in this paper can provide a reference scheme for the design of high-performance circulator or isolator. © 2022 IEEE.