According to theoretical analysis,when vibration milling is used to prepare ultra-fine grains,the exogenic work leads to the material local deformation.When local stress exceeds critical shearing stress of material,the breakaway points are reached within the material and the inner energy is released,which quicken up the crack growth and form new surfaces.Then vibration energy transforms to heat energy,chemistry energy and surface energy of the new grains in the process of impact.Scanning electron microscope and transmission electron microscope images show that the average diameter of the grains becomes less and less as time consuming and its granularity approach gradually uniform.Xray diffractmeter results reveal that the lattice parameters,chemical constitution of the nano-particles are the same as raw material and no new phase appears.