The　eigenfrequencies　distribution　functions　were　studied　by　the　theory　of　electromagnetic　reflection　for　three-dimensional　microwave　cavities.　For　the　electrical-large　cavity,　its　eigenvalue＇s　average　density　function　accords　with　the　Wely　formula.　According　to　the　theory　of　wave　chaos,　the　normalized　nearest-neighbor　spacing　distributions　of　the　square　of　eigenvalue　satisfy　Poisson　distribution　and　Wigner　distribution,　respectively,　for　regular　and　complex　cavities.　Furthermore,　the　statistical　simulation　method　of　Wigner　distribution　was　established　with　random　matrix　of　Gaussian　orthogonal　ensemble.　The　numerical　results　are　consistent　with　theoretical　analyses.