In the paper, numerical analysis of thermal processes proceeding in a biological tissue is presented. The tissue is subjected to the external heat impulse and a 2D problem is taken into account. In order to determine the influence of variations of thermophysical parameters of the tissue on the value of tissue injury integral and the area of the lesion, a direct approach of sensitivity analysis is applied. The process of thermal injury formation is also analyzed. At the stage of numerical simulation, the boundary element method is used. In the final part of the paper, an example of numerical simulation is shown.