Abstract：The field-pattern of various resonant modes of two-dimensional photonic crystal microcavity structure is investigated using the effective-index model. Results show that increasing optical thickness can lead to good photon localization. The refractive index and optical thickness of materials are tested at various values of the refractive index, film thickness, and effective index to achieve good photon localization. The effect of optical thickness on the modal the resonance characters are analyzed. It is important to find a mechanism through which to control the optical-field distribution and maintain single-mode vibration on a large scale. A two-dimensional photonic crystal, which has periodically-distributed refraction coefficient, is proposed as a potential choice. This paper also indicates that for a photonic crystal structure with a small refractive index difference to acquire a good photon-restriction ability, it must not only rely on the total internal reflection generated in its own materials, but it also must employ an adequately thick layer of optically thick material. Through the above analysis, theoretical guidance has been provided for the design, preparation, and application of such photonic crystal micro-resonators.