Currently, problems associated with energy and environment have become increasingly serious. Producing hydrogen, a clean and renewable resource, through photocatalytic water splitting using solar energy is a feasible and efficient route for resolving these problems, and great efforts have been devoted to improve the solar‐to‐hydrogen efficiency. Light harvesting and electron–hole separation are key in enhancing the efficiency of solar energy utilization, which stimulates the development of new photocatalytic materials. Here, recent advances in material design for photocatalytic water splitting are presented from a theoretical perspective. Specifically, aiming to enhance the photocatalytic performance, general strategies of materials design are discussed, including codoping and introducing a built‐in electric field to improve the light harvesting of materials, reducing the dimension of materials to shorten the migration pathway of carriers to inhibit electron–hole recombination, and constructing heterojunctions to enhance light harvesting and electron–hole separation. Future opportunities and challenges in the theoretical design of photocatalytic materials toward water splitting are also included.