Early determination of the thermal lesion degree in case of scald accelerates the treatment process and increases its effectiveness. The thermal lesion degree can be evaluated by determining the temperature difference between healthy and injured areas of biological tissue. For this purpose, a model of biological tissue in the form of a multilayer structure can be used. Heat exchange processes in such a structure are described by a generalized thermal model. Such structure contains conditionally flat heat sources located in each layer, which have the form of a developed network of blood vessels. The considered model of biological tissue quite accurately describes the heat exchange processes in body tissues. The article considers heat exchange processes that take place in biological tissue and a number of assumptions that should be used to mathematically describe these processes were identified. During the analysis of heat transfer process, the equations of temperature distribution in the tissue layers and the boundary conditions that describe the thermal interaction of the model with the environment are determined. As a result, the model of the stationary thermal regime of a biological tissue fragment in the form of a generalized thermal model and a mathematical model of the temperature field distribution in this fragment is obtained. This model is determined by many parameters, which are divided into 3 groups: thermophysical parameters; structural and topological parameters; parameters of the blood vascular system. Models of the particular fragment thermal regime are unequivocally determined by a combination of these parameters. For the analysis of temperature in any point of biological tissue modelled part mathematical model of temperature field distribution in stationary mode was developed. This model allows reasonable approach to the thermal lesion degree evaluation on the basis of the surface temperature difference between healthy and injured areas of tissue.