Abstract: To control the quality of continuous casting round billets used for oil well pipes, a mathematical model based on slice moving method was developed for the solidification and heat transfer process of the round billets. Then, a mathematical simulation was done using the ProCAST software for the solidification process of the φ150 mm round billets of 37Mn5 steel. As a result, the predicted billet surface temperature is in accordance with testing results of industrial experiments. The simulation results showed that, on the conditions that the superheat is (20 ± 5)°C, with a drawing velocity 2.5 m · min^-1, the billet shell thickness at mold exit, the liquid core length, and the surface temperature of strand can all be controlled in appropriate range to prevent the billets from surface/internal cracks and ensure the casting safety with productivity improved.