To improve the bit error rate (BER) performance of physical-layer network coding (PNC) in asymmetric two-way relay communication systems, a new PNC scheme named combined orthogonal physical-layer network coding (COPNC) is proposed. In the scheme, the two source nodes employ orthogonal carriers; then the relay node employs orthogonal combination and broadcasts the combined signal to the two destination nodes. Analytical and simulation results show that COPNC can provide better BER performance when the channel conditions in the systems are asymmetric. Especially when the two uplink channels have different signal to noise ratio (SNR), BER of COPNC is lower about 3 dB than PNC. As a result, COPNC is very suitable to be used in two-way relaying communication systems with asymmetric uplink channels.