Abstract: In order to test the operation effect of grinding and separation process of lean magnetite af⁃ ter the transformation of 3# series full-size wet pre-concentration process in Yanshan Iron Mine，the whole process was investigated and analyzed. By means of chemical composition，iron phase and particle size screening analysis，the ore properties，mineral types and contents in each process，monomer dissociation de⁃ gree and the loss trend of useful minerals，gangue minerals and metals in the process are analyzed，and the operation status of each process is comprehensively analyzed and diagnosed. From the perspective of the op⁃ eration effect of the overall process flow，the production status of the 3# series is normal，and the concentrate yield and quality indicators basically meet the design requirements；However，after the overflow of the elu⁃ triation machine returns to the original process through the scavenging concentrate，it will cause problems such as increased circulation，low classification efficiency of the first stage cyclone and anti-enrichment， and there is room for further improvement in technical and economic indicators.

Key words: magnetite, grinding and classification, magnetic separation