A new defect structure of twodimensional magnetic-photonic crystal was proposed and applied to implement the threeport Yjunction circulator using a ferrite cylinder. External characteristics of the circulator were calculated by the plane wave expansion method and finite element method, the numerical results show that there is an agreement between the resonance frequency of microcavity constructed by a point defect in the 2D triangular lattice photonic crystal with those results of corresponding experiments. In the center frequency, the transmission efficiency of the circulator is the highest and there is no energy loss between output port and input port; the isolation and insertion loss of circulator respectively reach 23.2 dB and 0.003 7 dB. When frequency diverges from the center frequency, the transmission efficiency gradually decreases with increasing frequency offset, and the transmission characteristics of the circulator sharply deteriorated. This design of circulator with air as background, can overcome low isolation of circulator with an array of air holes, and solve the high loss from multiple ferrite cylinders, having obvious superiorities.