Abstract: The structure,separation principle and practical application of magnetic agglomeration gravity separator in Lizhu Iron Mine were described.The stress condition of magnetic-particle in magnetic agglomeration gravity separator is analyzed.The segregate and critical particle size is counted in different magnetic field.The practices indicate that in the case of lean iron ore and fine particle size ore,good separation results can be achieved and grade of iron concentration is increased which the percentage points is 1.26 and the increase of economic benefits can add up to RMB 8301000 yuan.