The main kinds of ores in the third mining area of Gongchangling iron mine are magnetite ore,hematite ore,partly oxidized ore.The contents of elements,mineral composition,distribution and size exist different influences on the character of mineral separation .Also,when the ore grinding size is big,the liberation degree of the magnetite ores is lower than the hematite ores,so its separation character is worse. But when the ore grinding size is smaller and smaller,the liberation degree of the two kinds of ores is closer and closer.Therefor,the magnetite ores need more grinding time to reach the similar mineral separation degrees.