With continued exploitation of mineral resources,the grade of run-of-mine ore is declining in some mine,the regrinding of middling is one of effective methods to increase the recovery of valuable elements in the ore.On the premise that the grade of rough copper concentrate is not lower than the indexes obtained on the producing site,the experimentation of selective regrinding of flotation middling(SRTM) was carried out,and the recovery of rough copper concentrate was increased from 86.99% to 89.93%.By experimenting,the process conditions of the new technology SRTM was sought after,such as pulp density and fineness of run-of-mine ore and middling,and reagent system.The principle of the new technology was studied by using reflecting microscope and liberation analysis,it was found that in the process of selective classification,regrinding and flotation of flotation middling coarser middling was grinded,classified and floated gradually and continuously,and a big closed-circuit cycle of grinding-floating was formed,the liberation degree of minerals increased,the flotation time of useful minerals extended,the efficiency of flotation increased.