Photonic crystal defect formed by the introduction of the defect was amplified in the gain medium and formed laser. To further clarify the laser characteristics of the defect, the matrix of the photonic crystals was theoretically analyzed and the characteristics of the photonic band gaps was obtained: the width of the optical band gaps increased as the number of cycles does, and a certain value exceed a certain amount of cycles was reached; the higher the value which determined by the width of the optical band gaps constant, the higher refractive index ratio; superposing different centers of the photonic crystal wavelength can effectively expand the optical band gaps range. The experimental result from the band gaps analysis reveals one-dimensional photonic crystals in the KTP, which negatively affects the photonic band structure of the wavelength response curve; the refractive index of the KTP increases as temperature increases, and then the direction of the long wavelength defect mode changes. The results of this study contributes to the theoretical and practical development of small light sources.