The catalyst plays a vital role in organocatalyzed atom transfer radical polymerization (O-ATRP). Catalysts in the ground-state, excited-state, and oxidized-state are in competitive equilibrium and mutually transforming status. However, the catalyst circulation process remains unclear in some respects. In this work, for the first time, a novel kinetic model is successfully developed to illustrate the exact circulation process and working mechanism of catalyst. For a broad range of conditions, the reported model presents excellent descriptions of kinetic behaviors of O-ATRP. In the polymerization process, the photolysis effect contributes to a small proportion of radical generation. Sufficient deactivation effect is crucial for controlled polymerization at the early stage of polymerization. And increased light intensity, halide ion concentration, catalyst loading and initiator concentration accelerate the establishment of catalyst dynamic equilibrium. Additionally, the excited-state catalyst quenches with an extremely high rate, leading to an immediate dormant period in on-off light switching regulation. The formulated results shed light on the catalyst circulation process and provide insights into the polymerization kinetics. (c) 2018 American Institute of Chemical Engineers AIChE J, 64: 2581-2591, 2018