The work aims to predict diffusion process of sherardizing in the method of numerical simulation. Based on analysis of sherardizing mechanism and formation process of Fe-Zn coatings as well as the Fick‘s second law, the sherardizing model with zinc as the main diffusion element was established in finite difference method. Variation of thickness and content of Zinc layer as a function of time and temperature in a certain temperature range and time was calculated and compared with the experimental measurements in the same conditions to validate reliability of this model. Firstly, the sherardizing samples were incubated at 360, 375, 390 ℃ for 4, 6, 8 hours, respectively. Secondly, phase thickness and Zn content of alloy layer in the samples were measured with scanning electron microscopy/energy-dispersive spectrometer and SmileView software, the measurements were compared with the results of numerical simulation. Content variation of various phases measured by the experiments coincided with calculation result. The phase thickness and total thickness of the alloy layer were close to calculation results. The model could favorably reflect the variation of Zinc layer content and thickness as a function of time and temperature, it could also be used to calculate and simulate variation of Zinc layer thickness and content in certain temperature range and certain time. Therefore, this model is of general validity to predict the zinc diffusion during sherardizing and can be used to guide the sherardizing process.