We　propose　a　scheme　to　directly　measure　the　Wigner　function　for　the　motion　of　a　trapped　ion.　Unlike　the　previous　scheme　[Phys.　Rev.　Lett.　78,　2547　(1997)],　the　present　scheme　works　in　the　intermediate-excitation　regime,　which　may　be　of　experimental　importance　in　view　of　decoherence.　The　scheme　can　also　be　used　to　perform　a　quantum　nondemolition　measurement　of　the　vibrational　energy　and　prepare　motional　Schrodinger　cat　states.