The invention discloses a sludge circular flocculation-membrane filtration reactor relating to the technical field of urban feedwater treatment and being used for treating urban drinking water with micro-pollution water quality. The sludge circular flocculation-membrane filtration reactor comprises a rapid mixing chamber, a flocculation reaction chamber, a membrane filtration chamber and a sludge regulation chamber and is matched with equipment such as a membrane production water/back washing water system, a cleaning system, a water feeding pump, a water feeding pipeline, a flocculant adding pump, a flocculant adding pipeline, a pipeline mixer, a residual sludge collection pump, a sludge backflow pump, a sludge agent adding pump, a sludge agent adding pipeline, and the like. The invention combines the advantages of two processes of membrane filtration and flocculation contact, ensures that the drinking water treatment process has the characteristics of large-sized flocculation group, good flocculation effect at low temperature, less use of flocculant, and the like by dint of the strengthened flocculation efficacy of the residual sludge, and can more efficiently control the membrane pollution as compared with other membrane processes, thereby being beneficial to long-term and stable running of a membrane filtration device.