Abstract: The field-pattern of various defect modes in the coaxial photonic crystal microcavity has been simulated using the numerical calculation method. The quality factor (Q-factor) and power loss of the microcavity have been calculated and the effect of geometrical parameters on the resonance characters was analyzed. Based on the defect microcavity, a periodic slow-wave system was constructed and the dispersion relation of this system has been discussed. The results indicate that a single defect mode can be gained in the microcavity and the resonance characters are sensitively affected by the longitudinal length of the cavity and the dielectric constant of medium rings. The slow-wave system has presented a good dispersion property and a relatively smooth slow-wave ratio curve with a wide range o