The structural stabilities, electronic and optical properties of SnS bulk, monolayer, and multilayers are systematically studied by using the first-principles calculations within the density-functional theory. Our calculated results indicate that monolayer SnS can be exfoliated from its bulk, and the process is similar to the fabrication of graphene. With the reduction of layer number, the structural stabilities of SnS nanostructures become weak and their band gaps increase due to the quantum confinement effect and the layer interactions. Therefore, the optical properties of SnS can be controlled by adjusting the layer number due to the fact that the optical properties of materials depend on their electronic structures. The main optical absorption peaks of SnS bulk and nanostructures originate from the electron transitions among the orbitals of Sn-5s, 5p and S-2p. Moreover, the optical absorption peaks of SnS show obvious blue shift when SnS structure transforms from its bulk to monolayer. The present study will contribute to the application of SnS materials in the solar cells.