Preparation of nanocrystalline 430L stainless steel powders by high-energy ball milling has been investigated. The samples were characterized by scanning electron microscope (SEM), X-ray Diffraction (XRD) and Matersizer. The SEM observation confirmed that the cold welding and fragmentation behaviors occurred during high-energy ball milling, which has important effect on the changes of the particle size. In the initial stage (0-10h), particle size increased and crystalline grain size decreased evidently. The mean particle size got to 330μm and the crystalline grain size got to 23nm for sample of 10h ball milling. In the later stage, the particle size decreased and the refinement of crystalline grain became difficult. The crystalline grain size of sample for 50h ball milling only got to 15nm.