A　series　of　experiments　on　damage　detection　of　large-diameter　(88　mm　diameter)　pipe　with　and　without　liquid　by　guided　waves　have　been　conducted.　Two　types　of　liquid　as　water　and　machine　oil　are　chosen　to　fill　in　pipe　for　detecting　the　influence　of　filler.　The　influences　of　liquid　types　on　guided　wave　propagation,　dispersion　and　attenuation　characteristics　have　also　been　studied.　The　mode　conversion　phenomenon　of　reflection　waves　exists　regardless　filling　state　of　pipe,　but　it　is　most　serious　in　water-filled　pipe,　and　weakest　in　vacant　pipe.　The　defect　wave　signal　could　be　distinguished　from　converted　wave　mode　by　time-frequency　analysis,　and　the　time　frequency　distributions　of　the　two　type　signals　are　different.　The　relationship　between　defect　length　and　defect　reflect　signal　strength　is　linear　in　vacant　pipe　and　nonlinear　in　liquid-filled　pipe.　With　the　defect　length　increasing,　the　defect　signals　of　liquid-filled　pipe　increase　too,　but　the　rate　of　increment　are　reduced.