This　work　aims　to　model　and　explore　the　competitive　mechanism　between　the　internal　flow　effect　(IFE)　and　external　current　effect　(ECE)　on　the　cross-flow　vortex-induced　vibration　(VIV)　of　a　free-span　submarine　pipeline　transporting　an　axial　internal　flow.　Considering　the　coupling　between　the　structure　and　fluids,　the　partial　differential　equations　of　pipeline　system　are　described　by　Euler-Bernoulli　beam　theory　coupled　with　the　wake　oscillator　model.　To　obtain　the　VIV　response　of　pipeline　at　different　internal　flow　and　external　current　velocities,　the　generalized　finite　difference　method　(GFDM)　and　Houbolt　method　(HM)　are　employed　for　spatial　and　temporal　discretizations　for　equations,　respectively.　The　results　indicates　that　when　the　IFE　is　not　accounted,　the　higher-order　VIV　modes　of　the　pipe　are　successively　excited　by　ECE.　Of　interest　is　that　coupling　flutter　phenomenon　between　even-order　and　adjacent　modes　will　occur.　Whereas,　when　the　fluid　inside　the　pipe　flows,　which　means　the　IFE　occurrence　to　be　observed,　the　coupled　flutter　phenomenon　disappears　along　with　significant　enlargement　of　the　amplitude　in　even-order　modes.　Meanwhile,　the　mode　transition　is　associated　with　internal　flow　velocity　and　a　continuous　change　in　the　external　flow　velocity.