A new defect structure of two-dimensional magnetic-photonic crystal with dielectric cylinders is given and a four-port cross-shaped circulator using five ferrite posts is envisaged. Based on the agreements between the resonance frequency of micro-cavity constructed by a point defect in the two-dimensional (2D) square lattice photonic crystal with those numerical results of related literatures, external characteristics of the circulator are calculated by the plane wave expansion method and finite element method. The results show that at the center frequency, the isolation of circulator is up to 23.49dB and the lowest insertion loss is 0.0281 dB; when frequency diverges from the center frequency, the transmission characteristics of the circulator deteriorate gradually with increasing frequency offset. This design of circulator with only one ferrite cylinder in the waveguides, which solves the high loss from multiple cylinders.