Abstract: In order to study the photon localization property of photonic crystal, the localized field distribution of defect modes was computed by means of the optical transmission matrix method.The concept of relative localization length was introduced, which represents the degree of the localization of photons.The shorter the length, the more stronger the degree, and vice versa.The results show that the localization of photons in the structure with a defect layer bordering on high refractive index layers is stronger than that bordering on low refractive index layers.For the former structure, if the condition of resonance Bragg scattering or Mie scattering was satisfied, the relative localization length become smaller.