Silicene is a two-dimensional honeycomb lattice formed by a monolayer of silicon atoms, which has similar electrical properties to those of graphene. Silicene attracts much attention due to its relatively large spin-orbit coupling. The transport properties through a silicene quantum wire controlled by a gate are studied by using the non-equilibrium Green function formalism. A pair of gapless and spin-polarized edge states appears only when the gate voltage is strong and the silicene quantum wire has perfect zigzag or armchair boundaries in which additional silicon atoms are absent. Moreover, the edge states controlled by gate are spin valley-polarized, that is, the directions of spins are opposite in different valleys, which is different from that of the edge state at the interface between the silicene and vacuum. These results can be helpful to design and fabricate the practical silicene nanostructure.