Defect engineering of semiconductors provides an effective strategy for improving photocatalytic performance without doping alien elements. Understanding the defect and defect-related photocatalytic activity of semiconductors could lead to new horizon in the rational design of photocatalysts for practical applications. Herein, novel oxygen-deficiency contained perovskite CaCu3Ti4O12 with tunable structures of cube, nanoparticle and octahedron were for the first time synthesized via a feasible molten salt reaction approach depending on halogen anions of employed salts la (X = F, Cl and Br). Formation mechanisms of the different structures were revealed on the basis of innate characters of the selected halide anions. Assorted shapes display strong visible light absorption, which is interconnected with Ti displacement and oxygen deficiency. The photocatalytic performances of those three homologues were evaluated by an antibiotic degradation under visible light illumination. A superior photoefficiency is achieved for octahedron shaped crystal, which reduces 95.86% total organic carbon within 60 min and exhibits the reaction rate normalized to surface area of 1.261 x 10(-2) g min(-1) m(-2), approximately 3.687 and 3474 times larger than its counterparts. The outstanding degradation efficiency is ascribed to the synergetic roles of effective charge transfer, oxygen deficiencies and critical roles of active radicals resulting in carrier separation and efficiency enhancement. This work provides fundamental understanding of the morphology tailoring and defect controlling towards exploring new generation of visible light photocatalysts for environment and energy applications.