Introducing a parameter called perfect factor,we investigated the operating conditions for the existence of perfect multi channel filtering of three cell complex period photonic crystals with the optical transmission matrix method.It is found that the multi channel filtering properties become more perfect as the ratio of the optical length of the high refractive index dielectric in the photonic crystal to that of the low refractive index dielectric goes away from the value 1.Also,it becomes more perfect when the angle of wave incidence increases.Under proper operating parameters,quite perfect multi channel filtering properties,corresponding to a perfect factor of 10 -4 ,can be obtained with the complex period photonic crystals.