One-dimensional magneto-optical photonic crystals with a dielectric defect layer, which is composed of dielectric layers and magnetic layers alternately, is designed. Non-reciprocal transmission of electromagnetic wave can be achieved when the external magnetic field in opposite directions are applied to the magnetic layers existing at both sides of the defect layer. The transmission spectra of the structure are analyzed by using the modified transfer matrix method. The results show that when the thickness of the defect layer changes, multiple non-reciprocal channels will appear in the photonic crystal photonic band gap in a certain wavelength range. The larger of the thickness of the defect layer is, the smaller of the spacing between adjacent channels is, and the number of channels that can be accommodated in the forbidden band is greater. Seven non-reciprocal channels in the photonic band gap can be achieved when the thickness of the defect layer is 7500 nm. The proposed structure can be used to fabricate multi-channel optical isolators, and expected to be widely used in areas such as density wavelength division multiplexing optical communication technology and integrated optical circuit system.