The SAG（semi-autogenous） mill discharge grading is an important link in improving grinding efficiency of concentrator.The Straight-line vibrating screen classification was used in the SAG mill discharge grading of  a gold mine in Qinghai Province，this serious influenced the stability of the production run，due to the high failure rate of linear vibrating screen，low mill plant operation rate.By changing the linear vibrating screen to cylinder sieve classification，equipment operation rate increased by 1%，beneficiation cost savings of nearly 100 000 yuan.The results show that the trommel screen can achieve the same effect as the linear vibrating screen in the grading equipment of the semi-autogenous mill.Compared with the linear vibrating screen，the trommel screen has the advantages of low energy consumption，low cost，simple structure and convenient maintenance.Thus greatly reducing the labor intensity and equipment maintenance time，improve the dressing plant equipment operation rate.The transformation of the beneficiation plant to enhance the process indicators has the vital significance.