The submitted contribution is focused on the mathematical determination of temperature and thermal parameters depending on the heat removal from solidifying steel in the mould, respectively in the primary zone during continuous casting of steel. The main task of primary cooling is primarily the heat dissipation from solidifying steel, therefore the knowledge of temperature fields in the billet and mould is important. As part of the research evaluating the thermal work of the mould, the dependencies of the heat flux density between the steel and the cooling water in the mould were expressed in the primary cooling area. For determining the intensity of heat removal from solidifying steel, parameters of cooling water and temperature gradients along the height and circumference of the working surface of the copper insert of the circular cross-section mould with a diameter of 410 mm and a length of 600 m were used. The research of thermal processes was carried out for two grades of steel, which characterise the group of most frequently cast types of steel. Temperature and thermal parameters were determined for solidification and cooling for steel with a carbon content of 0.17 wt% (grade A) and 0.49 wt% (grade B). The casting speeds of steel were chosen in the range from 0.46 m·min–1 to 0.62 m·min–1. The obtained dependencies will be further used for numerical simulation