By means of high energy shot peening (HESP) to a pure iron cylinder, a nanocrystalline surface layer without oxidation, porosity and contamination was obtained. The thickness of the nanocrystalline surface layer was more than 100μm and the average grain size was about 50nm. The pulse pressure diffusion (PPD) and constant pressure diffusion (CPD) were used to diffuse nickel into nanocrystalline iron at 850℃ on Gleebl 1500 . Experimental results showed that diffusivity of Ni in the nanocrystalline Fe is 1 orders of magnitude higher than that in coarse-grained Fe and 1 orders of magnitude higher than that using CPD. The enhanced diffusivity of Ni may originate from the following three reasons : (1) pulse pressure can break the metalic compound formed during diffusing which may block the diffusion of Ni to inner nanocrystalline Fe; (2) a considerable amount of triple junctions and (3) a large volume fraction of non-equilibrium grain boundarie(GBs) in the present nanocrystalline Fe sample processed by means of the HESP technique.