The characteristics of a waveguide y-junction circulator with an off-centred circular ferrite post were analyzed by the point-matching method based on coordinate transformation. The influence of the ferrite post displacement from the junction center on the circulator performances was discussed. It can be concluded from the numerical results that: (1) The circulator with an off-centred ferrite post can be used as an excellent y-junction isolator with low insertion loss,low VSWR and high isolation ; (2) The asymmetrical performances of an asymmetrical waveguide y-junction circulator can be corrected by the ferrite post displacement.