Abstract: It is studied the defect mode and bistability properties of a nonlinear medium sandwiched between Bragg reflectors composed of one-dimensional photonic crystal by numerical calculation and theoretical analysis.The influence of defect layer thickness and quasi-periodic Bragg reflectors on defect mode and bistability is discussed.It is revealed that the defect mode shift to lower frequency when the increasing thickness of defect layer or refractive index of Bragg reflectors.Hence microcavity resonant mode is superposition with incident wave mode at lower incident intensity,and produce the bistability with lower threshold.The numerical calculation results accord with theoretical analysis.It is significant for design of photonic crystal microcavity.