The　system　complexity,　detection　probability　and　average　acquisition　time　are　the　most　important　performances.　This　paper　proposes　a　novel　method　to　reduce　false-alarm　probability　and　Improve　these　performances,　which　utilizes　the　changes　or　power　spectral　density　between　in-sync　and　out-of-sync,　and　uses　the　difference　of　signals　In-band　and　out-of-band　instead　of　the　signals　in-band　as　the　Inputs　of　threshold　comparator.　What　is　more,　this　paper　also　proposes　an　adaptive　threshold　adjustment　technology,　which　bases　on　the　average　power　spectral　density　of　received　signals.　At　last,　the　simulation　results　are　given.