We　propose　a　scheme　to　prepare　Fock　states　for　the　vibrational　motion　of　a　trapped　ion.　Unlike　previous　schemes,　the　present　scheme　works　in　the　mediate-excitation　regime,　in　which　the　corresponding　Rabi　frequency　is　equal　to　the　trap　frequency.　Thus,　the　required　time　is　greatly　shortened,　which　is　important　in　view　of　decoherence.