A system and method to prevent an oxidizer overheating using cold side bypass for a volatile organic compounds (VOCs) treatment system with a series rotor are described, which is mainly used in the organic waste air treatment system. The system is equipped with a thermal oxidizer (to), a first heat exchanger, a second heat exchanger, a third heat exchanger, a first cold-side transporting pipeline, a first adsorption rotor, a second adsorption rotor, and a chimney. A cold-side proportional damper is installed between the first desorption-treated air pipeline and the first cold-side transporting pipeline, or it is installed on the first desorption-treated air pipeline. When the VOCs concentration becomes higher, the cold-side proportional damper can regulate the airflow to adjust the heat-recovery amount or concentration, when treating the organic waste air, it can prevent the thermal oxidizer from being overheated due to high oxidizer temperature, and protect from thermal oxidizer shut-down.