The transmission spectrum of quasi-periodic 1-D photonic crystal containing two defects was calculated by transfer matrix method,and the emphasis was put on the analysis of the characteristics of the defect mode.The results indicate that:When the refractive index of the two defects layer is 1,the transmission spectrum of the photonic crystal has a band-gap containing all wavelength of the visible light,but when the refractive index of the two defects layer is 1.1,a defect mode appears in the original band-gap,the location and the peak of the defect mode vary with the refractive index of two defect layers.The greater the refractive index is,the longer the wavelength corresponding to the defect mode location is,and the peak of the defect modes is also greater.The use of this feature of the defect modes,you can design a smoke micro-sensor.