Heat stability of nanostructure can be related to alloy element, in order to investigate the effect of external element diffusion, asymmetrical rolling was adopted to roll 3% non-oriented silicon steel to realize the surface nanocrystallization, heat-treatment with different parameters was carried out for the rolled sheet in vacuum and Si+1% (mass fraction) halide powder respectively, and different techniques were used to examine the microstructural evolution, phase transformation and Si distribution along the depth. Experimental results show that nanocrystallines about 10~20 nm in size with random orientations form in the top-surface layer after the asymmetrical rolling with the mismatch speed ratio 1.31 and rolling passes 20 for 91% reduction. In the heating process in vacuum, the recrystallization temperature of the nanocrystallines in the top surface layer of the rolled sheet was found to increase obviously comparing with that obtained after keeping at this temperature for a long duration. In the heating process in Si+1% halide powder, a further enhancement of the recrystallization temperature was observed for the nanocrystallines in the top surface layer of the rolled sheet due to the fastly diffusion of Si atoms along the defaults, then the larger volume fraction of grain boundaries can act as fast diffusion channel at higher temperature (750 ℃), that can accelerate the diffusion of Si atoms, therefore dense compound layer can be obtained within shorter duration and with lower fraction of halide (acts as activator).