Abstract: in this paper,based on Mg-Mn ferrite Material and simulation by the HFSS,a Ku-band broadband miniaturized SMT microstrip circulator was designed and fabricated successfully; In order to realize the miniaturization of the device and satisfy the requirement of large bandwidth,a microstrip gyro-magnetic junction with comb structure is designed based on the traditional double-Y junction theory and the three-dimensional full electromagnetic simulation of HFSS; In order to realize SMT packaging and compatible with the fabrication process of microstrip circuit thin film on ferrite,the air-filled metal through-hole structure between bottom microstrip and circulator microstrip was designed in this paper,and optimized through-hole structure by HFSS; In order to realize the independence of circulator and non-interference with other components in the system,St12 metal with high permeability was used as shielding cover,this can shield electromagnetic signals and realize magnetic conduction at the same time.Finally,the device was fabricated and tested according to the optimal design results. the test results show that the SMT circulator designed in this paper has a full package size of 8 mm* 9 mm* 4 mm,this circulator bandwidth reaches 20%,Loss＜0.7 dB,Isolation＞18 dB,VSWR＜1.35,The circulator has no electromagnetic interference with the outside world,and it is suitable for large-scale automatic mounting.