Abstract: A multi-stage loop reactor, employed in various gas-liquid or gas-liquid-solid chemical reaction systems, which comprises a reactor body, draft tube(s) inside the reactor body, and a gas distributor at the bottom of draft tube. The draft tube can include one or more sections. The multi-stage loop reactor of the present invention has a higher mass transfer rate because the different phases are well mixed throughout the reactor, and the gas bubbles are distributed evenly everywhere. The reactor of this invention can be extensively applied in various gas-liquid or gas-liquid-solid reaction processes including the oxidization process, hydrogenation process, hydrocracking process, coal liquification process, fermentation process, hydrocarbon processing process, and biological treatment of waste water, etc.