Abstract: A moving bed biofilm reactor includes a tank body, a first tube, a second tube, a first guiding structure, a second guiding structure and a return pipe. A reaction zone is formed in the tank body by the first tube and the second tube. A three-phase separation zone is formed in the tank body by the first guiding structure and the second guiding structure. By using multi-layer horizontal water curtain disturbances formed by the first tube and the second tube, fluid contaminant could be well mixed in the reaction zone. Thereupon, gas desorption from bio carriers can be increased, the possibility for micro organisms to attach the bio carriers can be raised, the guiding of gas emission can be improved, and thus performance of the fluid treatment in the anaerobic biological process can be substantially enhanced.