Abstract: Aiming at the problems of low new efficiency of grinding products of ϕ7.32 m× 11.28 m large ball mill in Lu ming Molybdenum Industry,such as low new addition efficiency of -0.074 mm and +0.20 mm,low content of 0.20~0.023 mm and 0.15~0.038 mm,based on the mechanical properties of ore and the distribution of particle size composition,the maxi mum medium size is obtained by using the semi-theoretical formula of ball diameter.The optimum medium is determined as steel section by laboratory research,and the initial installation scheme is recommended as mass ratio of ϕ50 mm×60 mm、ϕ40 mm×50 mm、ϕ30 mm×40 mm、ϕ20 mm×30 mm of 15%∶40%∶30%∶15%.The laboratory test results show that compared with the on-site scheme,the yield of -0.074 mm,the intermediate optional grain size and the intermediate easy-to-select grain size are improved when the recommended steel section initial assembly ratio scheme is adopted.The results of laboratory scale test show that compared with the field scheme,the yield of -0.074 mm increases by 6.92 percentage points,the yield of the inter mediate optional grain size and the intermediate easy-to-select grain size increases by 4.47 and 5.37 percentage points respec tively when the recommended steel section initial assembly ratio scheme is adopted.The discrete element simulation shows that the initial assembly ratio of the recommended steel section is significantly improved compared with the total energy and effec tive collision energy of the field initial assembly ratio,and the medium-ore collision energy is increased by 6.22 percentage points,which further confirms that the optimization effect of the scheme is obvious.