Abstract: In practical communication of two-way relay channel, the transmission rate is always asymmetric because of the asymmetric channel quality, transmission power and rate requirement. This paper proposes two schemes of asymmetric transmission based on physical layer network coding. First one is cascaded channel coding, and second one is subset coding and subset modulation. The two schemes take advantage of the linearity of convolutional code so that the relay node can decode directly the superposition signal into the XOR bits. Simulation results show that the asymmetric schemes not only improve the transmission validity by increasing system capacity, but also guarantees the transmission reliability by lowering BER.