Photonic crystals are suitable for optoelectronic integration, for their sizes are comparable to their working wavelength.Optical diode is one of the fundamental elements in integrated optics.It allows optical signal to transmit only in one direction.On the basis of total reflection principle, a 2-D square-lattice photonic crystal heterostructure for unidirectional transmission of dual-polarization light is designed.The heterostructure consists of two photonic crystals.One is silicon rods immersed in silicon dioxide background, the other one is silicon dioxide rods immersed in silicon background.The transmission property of this structure is studied.The results show that, this structure can easily achieve unidirectional transmission for dual-polarization light wave centered in 1 550 nm.Furthermore, the band maps of two photonic crystals for different polarization modes are also analyzed.It is found that, the unidirectional transmission of this heterojunction does not depend on bandgap mismatch any more, owing to the total reflection on heterojunction interface.Finally, the period of heterostructure and the width of output waveguide are optimized, which improves the performances of optical signal unidirectional transmission for TE and TM mode, enhances the contrast ratio and broadens the bandwidth of unidirectional transmission.