A new model for the simulation of the converter steelmaking process was developed after a detailed study of existing thermodynamic and kinetic models and approaches. This model is based on the coupled reaction model, which includes both thermodynamic and kinetic calculations. The thermodynamic part includes the calculations of: Equilibrium constants of the oxidation reactions, the activity coefficients of hot metal components applying the Wagner-Lupis-Elliot method, and the activity coefficients of slag components using the collective electron theory. The kinetic part comprises the calculations of: The rate constant of carbon monoxide gas generation, the total mixing energy and the mass transfer coefficients in the metal and slag phases. The mass transfer coefficient in the metal phase is defined by the technological parameters of the process and the specific geometry of the converter. The new BOF model comprises sub-models for the dissolution of lime, scrap and other charge materials, the interfacial area, the post combustion and the dust formation. Part of the new model is a heat balance, which includes the separate calculation of the heating and dissolution of each charge material portion. The considered sub-models can be improved, replaced and tuned according to the technological features of a specific converter. The developed model allows the simulation not only of end blow temperature, and composition of steel and slag, but also the behaviour of these parameters as well as dissolution and melting of charge materials during the heat. End blow parameters can be accurately defined by the use of tuning parameters for each specific converter. The final version of the model was accomplished as standalone software with the graphical user interface.