Propagation　characteristics　of　longitudinal　modes　in　water-filled　steel　pipe　are　studied.　Longitudinal　modes　at　l60kHz　and　195kHz　are　excited　and　used　to　detect　a　artificial　circumferential　defect　in　a　water-filled　steel　pipe.　Results　show　the　branching　parts　of　unperturbed　L(0,2)　mode　with　low　dispersion　and　attenuation　are　suitable　for　defect　detection　in　water-filled　pipes　for　its　energy　propagates　mainly　in　pipe　wall　and　the　present　of　water　don＇t　affect　it　seriously.　However,　longitudinal　modes　at　certain　frequency　ranges　are　unsuitable　to　detect　defects　for　their　energy　propagates　mainly　in　water　and　they　disperse　greatly.