The invention provides a dual-band UV photo-decomposing intelligent-cycle-control composite treatment system of waste gas and belongs to the technical field of environmental protection. Since UV-C andUV-D featured differently in photo-decomposing mechanisms of harmful ingredients and ozone generation mechanisms, reasonable optimal layout and configuration are carried out; cyclic treatment of waste gas is controlled intelligently through the various composite means, such as filtering, adsorbing, photo-decomposing, oxidizing, and catalyzing. At the premise of ensuring waste gas treatment speed,the running quantity of UV lamp tube units is decreased as far as possible and their running time is balanced; the content of harmful ingredients and the content of ozone in the emitted waste gas aremaintained within the reasonable threshold range. Processing speed, efficiency and effect of the system herein are increased effectively; maintenance workload and operation cost can be decreased greatly; the service life of each component of the system is extended. In addition, the system herein also has the advantages of simple structure, low cost, good operation reliability, good maintenance and installation convenience and the like, is widely applicable to purification of various waste gases, and allows environmental protection effect to be improved effectively.