Considering　an　OFDM　modulation　based　system　including　one　pair　of　legitimate　transceivers　and　one　eavesdropping　node,　we　design　a　physical　layer　security　transmission　algorithm,　which　first　sorts　the　subcarriers　in　terms　of　the　legitimate　channel＇s　quality　and　then　sends　one　half　of　original　information　bits　over　the　first　half　better　subcarriers　while　the　XOR　results　of　two　halves　of　information　bits　over　the　rest　subcarriers　with　poorer　channel　quality.　This　algorithm　can　achieve　perfect　security　without　reducing　the　spectrum　utilization　of　the　system.　Further,　in　order　to　improve　bit-error-rate　(BER)　performance　of　the　legitimate　receiver,　the　subcarrier　power　is　optimally　allocated　to　minimize　the　BER　of　the　legitimate　receiver.　The　simulation　results　show　that　the　proposed　scheme　could　obtain　better　performance　at　the　legitimate　receiver　under　the　condition　of　perfect　security　when　the　ideal　channel　reciprocity　at　both　ends　of　the　legitimate　transmission　is　assumed.　The　designed　power　distribution　scheme　can　further　reduce　the　legitimate　receiver＇s　BER　effectively.　©　2018　IEEE.