Inspired by the leaf/vein structure of leaves which effectively supports the photosynthesis of green plants, a nano-leaf/vein bionic structure of self-assembled TiO2/MoS2 composites is applied to induce the reversible photochromic reactions of methylene blue (MB) for the first time. This reversible photochromic phenomenon gives a novel performance for the TiO2/MoS2 composites and expands their applications. Similar to the case where the natural vein network in leaves ensures the efficient material transfer and energy exchange for photosynthesis, the bionic internal MoS2 vein network in the composites ensures the efficient separation and directional transfer of photo-generated carriers to restrain the photocatalytic degradation reactions and to enhance the reversible photochromic reactions. Furthermore, the photosensitive applications of the TiO2/MoS2/MB systems with such a self-assembled nano-leaf/vein bionic structure are discussed with two typical photoelectric sensory models for both controllers and detectors.