Abstract: In the field of metal heat treatment, Fick's second law is discretized using the Crank-Nicholson method to analyze the differential scheme. Various mathematical models for the mass transfer coefficient β and the carbon diffusion coefficient D are collected. A program is written in C# to simulate the carburization process, and the results are compared with the actual layer-by-layer carbon content to identify the mathematical model suitable for gas carburization of 18CrNiMo7-6 material.