 The study comprehensively reviews point-defective metal-based photocatalysts for water splitting, focusing on understanding the defect's disorder effect on optical adsorption, charge separation and migration, and surface reaction. The controllable synthesis and tuning strategies of defective structure to improve the photocatalytic performance are summarized, then characterization techniques and density functional theory calculations are discussed to unveil the defect structure and analyze the defects-induced electronic structure change of catalysts and its ultimate effect on the photocatalytic activity at the molecular level. The challenge in developing more efficient effective metal-based photocatalysts is outlined, which may help further the understanding of the fundamental role of defect structure in the photocatalytic reaction process and guide the rational design and fabrication of highly efficient and low-cost photocatalysts. This article was authored by Yongcha Jian, Nisha Afsel, Luan Pan, and others.