The invention discloses a method for regrinding copper slag flotation middling. The first stage of fine-selected middling is conveyed to a slime dam through a submersible slurry pump and then conveyed to a swirler from the slime dam through a slurry pump to be classified, and large-grained slurry and qualified slurry are obtained through classification; the large-grained slurry enters a second stage of grinding to be reground, ground slurry then flows into a slime dam again, and therefore a closed-loop middling grinding is formed; the qualified slurry enters a first stage of rough selecting through a stirring barrel to continue to be subjected to flotation, and then regrinding of flotation middling is achieved. According to the method, valuable minerals are sufficiently subjected to monomer separation, and the feed size of slurry is increased; the valuable minerals are sufficiently subjected to monomer separation, floatability of the valuable minerals is enhanced, flotation foam is stable, and flotation workers can easily conduct operation. The copper concentration recovery rate is increased to 93.00%, the copper concentrate grade is improved to 25.00%, the copper content of tailings is reduced to 0.28%, and the phenomenon that sedimentation in a tank easily happens in the flotation process and a flotation machine is buried completely is eliminated.