We　propose　a　scheme　for　the　direct　measurement　of　Wigner　function　in　two-mode　cavity　QED.　The　atoms　are　sent　to　resonantly　interact　with　two　orthogonally　polarized　cavity　modes　in　the　presence　of　strong　classical　field.　The　probability　of　measuring　the　atom　in　the　ground　state　directly　gives　the　useful　information　of　the　cavity　field.　This　method　can　be　used　for　quantum　non-demolition　measurement　of　the　photon　number.　©　2010　Chinese　Physical　Society　and　IOP　Publishing　Ltd.