Propagation　characteristics　of　longitudinal　modes　of　ultrasonic　guided　waves　are　researched　for　the　defect　detection　on　helical　bellows.　The　finite　element　models　of　helical　bellows　are　created　using　commercial　package　Abaqus　firstly　and　the　results　of　numerical　simulation　with　a　circumferential　crack　have　been　calculated.　Furthermore　experimental　research　is　developed　using　electromagnetic　acoustic　transducer.　The　sinusoidal　tone　burst　modulated　by　a　Hanning　window　with　20　cycles　is　used　for　exciting　ultrasonic　longitudinal　guided　wave　mode　L(0,　2)　at　240　kHz　in　helical　bellows　to　detect　artificial　defects.　Single　transducer　is　applied　for　the　excitation　and　reception　of　L(0,　2)　modes　simultaneously.　The　crack　in　helical　bellows　can　be　identified　and　Uncertainty　of　measurement　result　has　been　calculated.　The　finite　element　analysis　and　experimental　results　show　that　it　is　feasible　and　effective　to　detect　defects　in　helical　bellows　based　on　ultrasonic　guided　wave　technology.