Abstract: Analyzed the elements responsible for the excessive ovality of the shell as rolled by the semi-floating mandrel mill.As a result,it is concluded that the problem of the said excessive shell ovality is brought about jointly by such elements namely,insufficient lubrication of the mandrel,poor surface quality of the operational tools,and improper setting of the process data.Accordingly,the ovality can be well reduced by means of bettering the lubrication conditions of the mandrel,and appropriately distributing the deformation amounts.