Owing to superior optoelectronic performance, halide perovskite-based materials have been widely applied in energy conversion systems such as solar cells. However, the halide-perovskite-based photoelectrochemical systems with the halide perovskite materials photoanode directly placed in aqueous solution receive insufficient attention. In this manuscript, for the first time a photoelectrochemical setup based on a dye-sensitized CH3NH3PbI3 photoanode directly immersed in water solution is demonstrated. The photoelectrochemical performance in the aqueous solution under the visible light irradiation is activated by a simple deposition of commercial dye on halide perovskite surfaces. The interfacial structures of the molecule/perovskite hybrid systems are analyzed via the density-functional theory calculations, indicating effective passivation of multiple potential surface charge traps. This study helps the fundamental understanding of the halide perovskite materials in aqueous environment, and highlights the concept of dye-sensitized halide perovskite photoelectrochemical system, which combines the virtues of dye-sensitized systems and halide perovskite materials for energy conversion applications.