Digital　modulation　techniques　is　a　very　important　method　of　realizing　modern　communication.　The　showing　up　of　Digital　modulation　techniques　promoted　the　development　of　modern　communication..　Research　on　digital　communications　modulation　theory,　provide　an　effective　modulation,　compressed　signal　transmission　band,　increase　channel　multiplexing　efficiency,　improve　signal　transmission　reliability,　has　important　significance　in　practice.