Abstract: Unidirectional optical transmission，also named optical diode，it permits optical wave to transmit from one incident direction while prohibit it when wave incidents from the reversed direction. It is one of the most important optical elements of the optical calculation and optical connections. While in linear and non -magnetic material system，the optical wave has to obey the reciprocity principle of the optics and the propagation path must be reversible. So it raises the questions that: Whether the unidirectional transmission can be obtained in linear and non -magnetic material system? If the answer is yes，what is the obtaining way? And what is the relationship　between the reciprocity principles and the unidirectional transmission in linear and non-magnetic material system? In this paper，the unidirectional transmission effect is obtained at multiple frequencies based on the guided mode resonance occurred in the substrate of a dielectric grating inspired by grating diffraction. And taking it for an example，we prove that in linear and nonmagnetic system，asymmetric optical transmission is also available and the reversibility of light is still effective. Besides，through further analysis，it is found that in this kind of linear and on-magnetic system，the unidirectional optical transmission is attributed to the asymmetric propagation channels of the optical path.

Key words: unidirectional optical transmission, reciprocity principles of optics, channel effect