The invention provides a mixed-stirred Fenton reactor. The mixed-stirred Fenton reactor comprises a reaction tank, a sedimentation tank and a water outlet weir, wherein the reaction tank is transversely divided into a middle area and side areas which are located at the two sides of the middle area, a stirring device is arranged in the middle area of the reaction tank, gas distributing devices arearranged at bottoms of the side areas, exhaust holes are formed in the reaction tank, and the sedimentation tank is located above the middle area of the reaction tank. The stirring of raw water, agents and active particles is achieved in a mixing and stirring mode through the gas distributing devices and the stirring device, a plurality of longitudinal circulating flow fields can be formed in thereaction tank, the stirring intensity of the reaction tank is greatly improved, and the treatment capacity of the device is improved. The stirring, uniform mixing and active particle fluidizing of thereaction tank are achieved through internal circulation, thus, a complicated external circulation system and a water distribution device are not required, and the technical problems of the traditional Fenton fluidized reactors that the water distribution is non-uniform, blockage is easy and the like are fundamentally solved.