In　order　to　analyze　the　performance　of　aerostatic　guidways,　the　stiffness　calculation　equation　of　the　aerostatic　guideway　with　two-row　orifice　has　been　derived　by　gas　lubrication　theory.　For　the　complex　structure　of　the　motion　guideway　and　unloading　guideway,　the　frequency　of　the　whole　slides　in　machining　direction　with　gas　thickness　has　been　derived.　Wavelet　transform　as　a　means　to　process　the　measured　signal　of　workpiece　surface,　the　frequency　characteristics　of　gas　fluctuation　of　aerostatic　guideways　has　been　extracted　out　from　the　measured　signal,　and　the　errors　of　the　guideway　system　have　been　identified　according　to　the　power　spectral　density　(PSD),　and　this　provide　a　basis　for　the　identification　of　machine　tool　error.