Surface quenching of the rail steel using the laminar plasma jet can increase its service life, but the treatment parameters can only be determined by the experimental methods currently, which is time-consuming and laborious. If a simulation model for the surface quenching process can be established to quickly predict the variation of the temperature field in the surface quenching process and the hardness distribution within the hardened zone, the optimal treatment parameters can then be obtained rapidly. A numerical simulation model was firstly established by the finite element method to obtain the temperature distribution. Then the limit value of the carbon diffusion was determined by the hardness distribution obtained from the surface quenching experiment. After that, the Austenite transformation rate at each heating rate was determined using JMATPRO. Finally, a model for predicting the metallographic structure was proposed. With the numerical simulation model, the variation of the temperature field during the surface quenching process could be obtained. By selecting the nodes greater than the phase transition temperature (for example, 745 ℃ for the U75V rail steel), the width and depth of the hardened zone could be predicted. The prediction error was found to be within 8% errors compared with experimental results. By extracting the temperature change curve of the nodes in the hardening zone and substituting into the metallographic structure prediction model, the transformation of the austenite and martensite at each node position in the hardening zone could be calculated, and the hardness at the hardening zone could be predicted. A series of surface quenching experiments with different surface quenching parameters, e.g. including arc current, anode diameter, scanning speed, etc., were carried out. It was found that the hardness predicted by the proposed simulation model was in good agreement with the actual hardness, which verified the effectiveness of the proposed simulation model for the laminar plasma jet surface quenching of rail steel.