The　global　bifurcations　and　chaotic　dynamics　of　a　string-beam　coupled　system　subjected　to　parametric　and　external　excitations　are　investigated　in　detail　in　this　paper.　The　governing　equations　are　firstly　obtained　to　describe　the　nonlinear　transverse　vibrations　of　the　string-beam　coupled　system.　The　Galerkin　procedure　is　introduced　to　simplify　the　governing　equations　of　motion　to　ordinary　differential　equations　with　two-degrees-of-freedom.　Using　the　method　of　multiple　scales,　parametrically　and　externally　excited　system　is　transformed　to　the　averaged　equation.　The　case　of　1:2　internal　resonance　between　the　modes　of　the　beam　and　string,　principal　parametric　resonance　for　the　beam　and　primary　resonance　for　the　string　is　considered.　Based　on　the　averaged　equation,　the　theory　of　normal　form　is　utilized　to　find　the　explicit　formulas　of　normal　form　associated　with　one　double　zero　and　a　pair　of　pure　imaginary　eigenvalues.　The　global　perturbation　method　is　employed　to　analyze　the　global　bifurcations　and　chaotic　dynamics　of　the　string-beam　coupled　system.　The　analysis　of　the　global　bifurcations　indicates　that　there　exist　the　homoclinic　bifurcations　and　the　Silnikov　type　single-pulse　homoclinic　orbit　in　the　averaged　equation　of　the　string-beam　coupled　system.　These　results　obtained　here　mean　that　the　chaotic　motions　can　occur　in　the　string-beam　coupled　system.　Numerical　simulations　also　verify　the　analytical　predications.　(C)　2006　Elsevier　Ltd.　All　rights　reserved.