In　this　paper,　the　coupled　bending-bending-axial-torsional　free　vibrations　of　rotating　blades　are　investigated　based　on　the　Euler-Bernoulli　beam　model.　The　coupled　partial　differential　equations　governing　flapwise,　edgewise,　axial　and　torsional　motions　are　derived　by　the　Hamilton＇s　principle,　wherein　three　types　of　velocity-dependent　terms,　namely　static　centrifugal　terms,　dynamic　centrifugal　terms　and　gyroscopic　coupling　terms,　are　focused.　The　ordinary　differential　equations　are　acquired　by　the　Galerkin　truncation,　and　the　natural　frequencies　in　all　directions　and　complex　mode　shapes　of　the　rotating　blades　are　analyzed　in　detail.　It　is　revealed　that　the　three　types　of　velocity-dependent　terms　have　different　effects　on　the　natural　frequencies.　The　natural　frequencies　are　noticeably　dependent　on　the　rotating　speed　and　preset　angle,　except　for　the　axial　vibration,　which　is　almost　immune　to　the　preset　angle.　The　complex　modal　motions　are　displayed　by　a　series　of　positions　of　the　central　line　and　free-end　cross　section　for　different　time　instants,　showing　the　coupled　vibrations　among　different　directions.