A sufficient and necessary optimality conditions is established for vector extremum problems with set constraint by applying the alternative theorem under generalized subconvexlike maps in orderd locally-convex Hausdorff spaces. Then, several optimality conditions are obtained for differentiable vector extremum problems with set constraint by applying the sufficient and necessary optimality conditions and the properties of the twice G-differentiable functions. And finally, the vector-valued Lagrange duality is obtained for the vector extremum problems.