Abstract: Silicon diffusing into iron base alloy is the main way to generate high silicon steel materials,however,the accurate analysis of silicon diffusion process is often considered as a whole diffusion effect,ignoring the microscopic diffusion differences in the grain and grain boundary(GB).In order to study the effects of grain boundaries for diffusion,a 3D microscopic model based on Voronoi structure is applied to simulate the process of intergranular and GB diffusion.The body diffusion coefficient (D_g) in the inner grain and material microstructural parameters can be provided by chemical vapor deposition(CVD) experiment,scanning electron microscopy(SEM) and energy spectrum analysis(EDS).Based on the material microcosmic parameters including grain boundary width and grain size,grain boundary diffusion coefficient (D_gb) of micro representative volume element can be obtained.The results of the experiment and simulation effectively show Silicon diffusion in Fe grain and grain boundary have obvious differences.The D_gb value is 3.3×10^-3 mm²/s,roughly 10³~10⁴ times as high as D_g.The silicon flux through grain boundary diffusion into alloy is reached nearly a third of total flux,so increasing the volumetric fraction of grain boundary can play an important role in improving efficiency and silicon quantity of CVD siliconizing.