The plasma surface hardening, as one of methods of surface treatment by heating sources with high power density, finds presently wide and effective application in conditions of short-series and single-part (including repair), and large-scale and wholesale manufacture. One of effective methods for research and optimization of the plasma surface hardening is the use of computer simulation. The complex mathematical model of steel parts hardening at high-speed plasma heating is presented in the article. Model includes mathematical description of steel parts heating and cooling, and also forming of their stress-strain state. The distinctive feature of the presented model is taking into account under modeling of phase transformations and plastic deformations. It allows to achieve the maximally adaptation of the simulation results to real physical characteristics of the process. The algorithm of model computer realization, based on the application of final elements method is offered.