The regrinding of middling is one of an effective methods to increase the recovery of non-ferrous metals.On the premise that grade of copper concentrate is not less than one obtained on the actual site in a copper plant,the mechanism of selective classification,regrinding and flotation of flotation middling(SCRFFM) was researched by means of Zeta potential analysis and infrared spectroscopy.In the process of SCRFFM,the useful minerals are grinded,classified and floated gradually and continuously,the big cycle of grinding-floating and a big grinding circuit can be formed,at the same time the SCRFFM can change the surface properties of the valuable minerals and increase their floatability,the copper recovery can be raised from 86.12% to 89.48%.