In　order　to　monitor　the　crack　propagation　of　the　structure　in　the　working　state　for　a　long　time,　an　operation　modal　analysis　method　based　on　pseudo-successive　data　is　proposed.　The　vibration　response　signals　of　the　cantilever　beam　under　white　noise　excitation　are　collected　and　the　modal　parameters　are　extracted　by　the　time-frequency　operation　modal　analysis　method　based　on　the　complex　Morlet　wavelet.　In　comparison　with　the　experimental　modal　analysis　results　of　hammering　method,　it　is　revealed　that　the　error　of　the　time-frequency　operation　modal　analysis　method　is　less　than　10　%.　By　setting　cracks　of　different　lengths　on　the　cantilever　beam,　the　vibration　response　signals　are　extracted,　and　the　modal　parameters　are　extracted　by　the　operation　modal　analysis　method　separately.　By　comparing　those　modal　parameters　above,　it　is　found　that　the　natural　frequencies　of　the　second,　the　fourth　and　the　sixth　orders　decrease　with　the　increase　of　the　crack　depth,　and　the　changes　of　natural　frequencies　show　the　monotonicity.　So,　it　can　be　used　as　an　index　for　quantitative　identification　of　crack　damage.　The　pseudo　continuous　data　monitoring　signals　of　crack　propagation　can　be　constructed　by　means　of　＂first　discrete,　then　continuous＂.　The　modal　parameters　changes　of　the　whole　crack　propagation　can　be　observed　in　one　time　plane　by　means　of　the　operation　modal　analysis　method.　Therefore,　the　effective　monitoring　and　diagnosis　of　the　structure　can　be　completed　in　case　of　excessive　data　of　long-time　vibration　monitoring　signals.　©　JVE　INTERNATIONAL　LTD.