A correlative demodulation and mapping scheme is proposed for the relay nodes in 2FSK two-way relay communication systems. The scheme ses superimposed signals with two branches, and samples the discrepancy to make a decision, which may be mapped to a binary bit. The decision thresholds are calculated according to the maximum posterior probability criterion. The relay nodes’ decision error probability and the bit error rate of the entire system are analyzed. Theoretical analysis and simulation results show that the relay nodes’ decision error probability and the system BER of the physical-layer network coding scheme using the proposed demodulation and mapping method are close to those of the traditional scheme and the network coding scheme, but the throughput is higher than the two.