In　this　paper,　the　channel　capacity　and　the　optimal　resource　allocation　scheme　for　Distributed　Alamouti　Space-Time　Code　based　on　Decode-and-Forward　(DF-DASTC)　protocol　are　investigated.　Using　the　degraded　relay　channel　model,　the　channel　capacity　of　DF-DASTC　under　fading　channels　is　derived.　To　maximize　the　capacity　of　DF-DASTC,　the　closed-formed　analytical　expression　of　the　optimal　power　allocation　scheme　with　fixed　bandwidth　allocation　is　derived　for　DF-DASTC.　Based　on　the　convex　optimization　theory,　the　multi-objective　optimization　issue　to　maximize　the　capacity　of　DF-DASTC　is　converted　into　the　general　single　objective　optimization　problem,　and　the　optimal　resource　allocation　scheme　with　variable　bandwidth　allocation　is　derived.　Both　theoretical　analysis　and　simulations　show　that　the　resource　allocation　scheme　can　significantly　increase　the　channel　capacity　of　DF-DASTC.　Moreover,　the　resource　allocation　scheme　is　a　generalized　method,　which　can　be　used　in　wireless　relay　networks　with　multiple　relay　nodes.