The effect of defect parity on the transmission properties of photonic crystal(AB)m(ACxB)n(AB)m is studied by transmission matrix method theory.The results show that the parity of defect number(n) only has effect on parity of defect modes(transmission peaks),namely,the parity of defect modes number is corresponding to n.The defect modes are closing to the band gap center with odd multiple increase of periodicity(x),but the number of defect modes are unchanged and arranged equidistant from each other.On both sides of band gap,the two groups of modes are closing to the band gap center with even multiple increase of periodicity(x),and the number of modes in each group depends on the periodicity(x).The effect of parity of the defect layer optical thickness(DC) on transmittance spectrum is also obvious.In the right band gap,the number of defect mode is increasing and the mode is moving towards low frequency direction with the increase of DC(DCDA,the number of defect mode in the left band gap is reducing with the increase of DC,and the defect mode is also moving towards low frequency.The law of defect parameters parity effect on transmission spectrum can provide theoretical reference for designing adjustable multichannel optical filter and optical switch,and also provide definite reference for theoretical study of photonic crystal.