An ortho-mode transducer (OMT) suitable for C-band communication system is developed to solve the problems of complex structure, complicated design and difficult debugging. The transmitter-receiver isolation in the 5.4 to 5.7 GHz frequency band is improved by using the quarantine characteristics between orthogonal waveguides and selecting the appropriate waveguide aperture size. The prototype is made and tested, and the results show that the VSWR of the straight-through port is less than 1.10, the VSWR of the coupling port is less than or equal to 1.15, and the transmit-receive isolation is less than -57.5 dB in the 5.4 to 5.7 GHz band, which proves that the design is effective and meets the requirements of C-band antenna and feeder equipment.