In　order　to　diagnose　the　unbalance　of　aerostatic　guideways,　displacement　and　acceleration　sensors　were　used　to　measure　the　vibration　signals　of　the　unbalance　of　the　aerostatic　guideways　caused　by　the　gas　fluctuation.　The　frequency　characteristics　for　the　unbalance　of　aerostatic　guideways　caused　by　gas　fluctuation　has　been　extracted　from　the　measured　signals　by　power　spectral　density,　and　the　basic　frequencies　of　the　guideway　system　have　been　diagnosed　according　to　spectral　characteristics,　in　agreement　with　the　results　calculated　by　the　corresponding　motion　equations　and　the　finite　element　method.