Highly efficient water splitting based on solar energy is one of the most attractive research focuses in the energy field. Searching for more candidate photocatalysts that can work under visible-light irradiation is highly demanded. Herein, using first-principles calculations based on density functional theory, we show that the two-dimensional silicon chalcogenides, i.e., SiX (X=S, Se, Te) monolayers, as semiconductors with 2.43-3.00eV band gaps, exhibit favorable band edge positions for photocatalytic water splitting. The optical calculations demonstrate that the SiX monolayers have pronounced optical absorption in the visible-light region. Moreover, the band gaps and band edge positions of silicon chalcogenides monolayers can be tuned by applying biaxial strain or increasing the number of layers, in order to better fit the redox potentials of water. The combined electronic properties, high carrier mobility and optical properties render the two-dimensional SiX a promising photocatalyst for water splitting.