Eavesdropping　in　wireless　communication　environment　should　be　suppressed.　However,　most　existing　schemes　ordinarily　focus　on　secrecy　rate　enhancement,　which　may　not　be　achieved　with　the　non-Gaussian　signals.　Therefore,　we　consider　this　security　problem　from　the　actual　signal　point　of　view.　On　the　basis　of　this　premise,　a　novel　scheme　is　proposed.　In　our　scheme,　each　original　signal　in　one　constellation　is　converted　as　a　transmitted　signal　in　another　constellation,　and　the　principle　of　this　variation　can　be　safely　told　to　the　user　without　being　learned　by　others.　With　this　conversion,　the　eavesdropper　is　difficult　to　restore　the　original　signals.　Performance　analysis　and　simulation　results　illustrate　that　the　proposed　scheme　is　efficient　for　physical　layer　security　improvement.