Propagation　characteristics　of　high　order　longitudinal　modes　of　ultrasonic　guided　waves　in　seven-wire　steel　strands　axe　investigated　theoretically　and　experimentally.　According　to　these　analysis　results,　proper　longitudinal　modes　are　selected　for　defect　detection　in　steel　strands.　Dispersion　curves　for　helical　and　central　wires　in　a　17.80　mm　nominal　diameter　seven-wire　steel　strand　are　numerically　obtained　firstly,　and　propagation　characteristics　of　high-order　longitudinal　modes,　such　as　wave　structures,　attenuation　and　dispersion,　are　analyzed.　In　experiments,　the　signals　of　ultrasonic　guided　wave　at　different　high　frequencies　are　excited　and　received　at　one　end　of　a　steel　strand　by　using　the　same　single　piezoelectric　transducer.　The　identification　of　longitudinal　modes　in　the　received　signals　is　achieved　based　on　short　time　Fourier　transform.　Furthermore,　appropriate　L(0,　5)　mode　at　2.54　MHz　is　chosen　for　detecting　an　artificial　defect　in　a　helical　wire　of　the　steel　strand.　Results　show　that　high　order　longitudinal　modes　in　a　high　frequency　range　with　low　dispersion　and　attenuation　whose　energy　propagates　mainly　in　the　center　of　the　wires　can　be　used　for　defect　detection　in　long　range　steel　strands.