The application of photonic crystal as micromirrors was emphatically investigated to calculate the photonic crystal band structure and band gap map, based on plane wave expansion method. The finitedifference timedomain was applied for analyzing the transmission characteristics of micromirrors constituted of the triangular lattice of dielectric cylinder structure to discuss the dielectric cylinder radius and lattice period effects on the reflectivity, and optimal results and parameters Were given. Photonic crystal ring resonant cavity constituted of dielectric cylinder can achieve monolithic integration, and realize the transmission of light in the air to substantially reduce the Kerr and Faraday effect, and the back scattering effects, etc. This study provides a new idea for highprecision resonant Gyro.