A gold smelter adopts graded grinding process to treat high sulfur gold concentrate.After grinding,the fineness is -0.037 mm accounting for 95 %,and the gold grade of cyanide residue is about 1.30 g/t.In order to explore the possibility of further reducing the gold grade of cyanide residue,the semi industrial test of Isa mill was carried out.The test results show that the grinding product is more distributed in 2 fine grain ranges of -5.21 μm and -9.86-＋5.21 μm after grinding by Isa mill,less distributed in ＋14.50 μm,and the ores are ground more evenly by Isa mill;the gold grade of cyanidation tailings is reduced from about 1.30 g/t to 1.10 g/t,and the silver grade is reduced from 11.30 g/t to 9.50 g/t,creating significant economic benefits.