This　letter　proposes　a　polarization　mapping　(PM)　for　polar　coded　modulation　with　physical　network　coding　(PM-PNC)　over　two-way　relay　channels　(TWRC).　The　achievable　information　rates　(AIRs)　of　the　mapped　bits　within　a　XOR　symbol　from　bit-wise　XOR　of　two　user　symbols　are　significantly　different,　since　the　users　adopt　non-uniform　PAM　modulation　to　avoid　mapping　ambiguity.　In　the　polar-coded　PM-PNC,　the　original　channels　associated　with　the　split　information　bit　channel　are　mapped　to　the　XOR　bit　stream　with　a　larger　AIR.　In　this　way,　the　achieved　rate　of　the　split　information　channels　can　be　maximized　and　is　illustrated　in　distribution　of　split　bit　channel　AIRs.　Simulation　results　show　that　the　proposed　PM-PNC　can　achieve　significant　performance　gains　of　more　than　0.5　dB　as　compared　to　the　bit-interleaved　coded　modulation　(BICM)　and　multilevel　coded　(MLC)　PNC　systems　over　Gaussian　and　block　fading　channels.