In　this　paper,　the　nonlinear　robust　H　infinity　control　is　investigated　for　nonlinear　course　control　systems　of　unmanned　surface　vessel　(USV)　with　uncertain　parameters　and　external　disturbance.　Firstly,　we　suppose　that　the　part　or　all　of　the　system　parameters　are　unknown　but　within　some　ranges,　due　to　the　effect　of　different　conditions　such　as　the　loading　of　ship.　Then,　the　course　system　is　modeled　as　a　polynomial　one　with　time　invariant　polytopic　uncertainty.　With　the　aid　of　parameter　dependent　Lyapunov　function　method　and　positive　polynomial　theory,　the　sufficient　conditions　are　given　for　stability　and　stabilization　with　H　infinity　performance.　These　conditions　are　formulated　in　terms　of　parameter-dependent　nonlinear　matrix　inequalities　which　can　be　verified　by　semidefinite　programming　relaxations　based　on　the　sum　of　squares　technique.　Finally,　simulation　results　show　the　effectiveness　of　the　approach.