Due　to　ultrasonic　guided　waves　propagating　in　composite　plates　are　characterized　with　skew　effect,　it　makes　there　exists　a　certain　discrepancy　between　experimentally　measured　and　theoretical　group　velocities.　Therefore,　it　is　needed　to　calibrate　the　amplitude　and　propagation　direction　of　group　velocity.　Dispersion　equation　of　ultrasonic　guided　waves　in　the　composite　plate　is　numerically　solved　and　theoretical　phase　velocity　dispersion　curves　of　S0　mode　at　different　directions　are　obtained.　The　amplitude　and　propagation　direction　of　group　velocities　of　S0　mode　are　calibration　based　on　group　velocity　calibration　principle.　Calibrated　and　experimental　group　velocities　are　well　matched.　In　experiments,　S0　mode　at　200　kHz　is　used　to　inspect　the　artificial　defect　in　the　carbon　fiber　composite　plate.　Experimental　results　show　accurate　localization　of　the　defect　can　be　achieved　by　using　calibrated　and　experimental　group　velocities　and　localization　results　by　using　these　two　types　of　group　velocities　are　consistent　with　each　other.　As　a　result,　the　abilities　of　defect　localization　and　identification　of　ultrasonic　guided　waves　can　be　effectively　enhanced　by　using　group　velocity　calibration　principle　in　composite　plates.　©　2012　Journal　of　Mechanical　Engineering.