Heterostructural photocatalysts with rationally aligned energy bands have been proved effective in diminishing the recombination of photo-induced excitons, thus leading to enhanced photocatalytic performance. However, the critical role of charge carrier behaviors and their quenching pathway in determining the overall photo catalytic performance are still not fully explored, which severely hindered the development for efficient photocatalysts. Herein, to further explore the essential principles of photocatalysis with heterostructures, a representative nano-regional photocatalytic heterostructure was constructed through uniform decoration of visible light activable BiOI nanodots on TiO2 nanorod assembled microflowers. With which as a well-known prototype of conventional heterostructures, a possible photocatalytic performance annihilation channel via reaction site self-quenching effect in photocatalytic heterostructures was experimentally evidenced for the first time. Based on our experimental results, we evidenced that excessive decoration with BiOI nanodots would result in severe self-quenching of their photocatalytic sites through highly probable charge carrier recombination between migrating electrons along TiO2 nanorods and reactive holes in adjacent BiOI nanodots. Such fundamental and experimental discovery is not limited to the current model and would shed light on the development of novel nano-regional heterostructures with high photocatalysis performance.