An　ultrasonic　inspection　technique　using　guided　waves　was　used　to　evaluate　the　detection　and　determination　of　the　exact　location　of　flaws　present　in　long　steel　pipes.　Theoretical　analysis　shows　that　guided　waves　have　the　disperse　and　multiple　modes　characteristics,　and　under　some　special　frequency　range　the　L　(0,2)　mode　is　the　most　suitable　mode　to　detect　the　pipe　defects.　Studies　of　flaw-detected　ability　with　the　use　of　some　guided　wave　modes　and　their　ultrasonic　attenuation　characteristics　were　experimentally　conducted.　The　experimental　results　also　showed　that　the　L　(0,2)　mode　was　the　most　effective　for　detection　and　exact　determination　of　the　flaw　location.