Deformation of round castings due to thermal and/or mechanical strain may lead to the occurrence of their ovality defects during continuous casting. Presently, ovality defect from thermal deformation have been effectively controlled in actual casting process with the application of more advanced equipments and more sophisticated control strategies. But the control of ovality defect from larger mechanical deformation still cannot satisfy the need of caster design or higher qualified rate of castings. It is shown that excessive hot pressure while strand passes through tension leveler, is the main reason to generate larger mechanical deformation. With consideration of the characteristics of round caster and the requirement of safety production, a theoretical calculated model based on mechanical deformation analysis has been developed in the paper to eliminate ovality defect specially from the over large hot pressure. Calculation analysis suggests that groove design of drive roller and range of round section sizes should be the important consideration for the determination of hot pressure, and there always exists an optimum value for hot pressure when the machine equipments of round caster have been designed and installed. The model can provide a useful guideline for casting engineers to design the groove of drive roller and to determine reasonable safe hot pressure. Reliability of the model analysis has been verified by industrial application on a newly built round caster.