Abstract: Based on mathematical model of carburizing, taking 1/4 section of sphere to build geometric model, the carburizing temperature and stress field of 20 steel were simulated by finite element analysis software ANSYS. Contour maps of temperature the field of the steel after carburizing for 60 s were obtained, and then stress field simulation results were got by taking the node temperature from temperature field simulation as a body to apply to structural stress analysis, and the simulation results were verified by experiment. The results show that simulated carburized depth after carburizing for 5 h was 0.13 mm, which was closed to experimental result of 0.11 mm, and thus the temperature field simulation results were proved to be reliable. The surface of 20 steel was in tensile stress state, the stress, continuously decreased further into the core, and the core was in stable stress state. After carburizing for 5 h, the surface stress reached 3.5×108 Pa.