Based　on　deeply　studying　and　analyzing　Hilbert-Huang　transform　(HHT),　a　so-called　semi-periodical-semi-symmetrical　method　is　presented　in　this　paper　to　deal　with　the　boundary　problem　resulting　in　error　during　the　process　of　the　empirical　mode　decomposition　(EMD).　It　is　proved　that　this　method　is　very　valid　and　has　high　precision　by　many　experiments　of　signal　simulations　and　comparison　between　the　results　from　this　method　and　those　from　the　EMD　method.