Vibration　control　of　an　axially　moving　string　system　consisting　of　a　controlled　span　coupled　to　a　tensioner　is　investigated.　The　axially　moving　string　system　is　divided　into　two　spans,　i.e.　a　controlled　span　and　an　uncontrolled　span,　by　a　tensioner　which　is　located　in　the　middle　section　of　the　string.　The　transverse　vibration　of　the　controlled　span　of　the　string　is　controlled　by　the　control　force　acted　on　the　tensioner,　and　the　constrained　point　is　considered　as　the　right　boundary　of　the　controlled　span.　The　adaptive　method　is　employed　to　design　the　controlled　law　for　ensuring　the　vibration　reduction　of　the　controlled　span,　and　the　asymptotically　stability　of　the　closed　loop　system　under　the　boundary　control　is　proved.　Results　for　the　response　of　the　controlled　string　under　initial　disturbance　and　excitations　are　presented,　and　the　effectiveness　of　the　controller　is　demonstrated　by　simulations.