Abstract: Analyzed with relevant 3D model are the wall-evening process of the piercing roll rolling zone，and the reduction zone and rolling zone of the roll of the Assel mill. And accordingly optimization design is performed. The optimized groove parameters are determined via production practice. The actual operation of the mill shows that 2.2° is the best piercing outlet cone. The wall thickness accuracy and inner surface quality of the workpiece during piercing and rolling processes can be enhanced，and the inner spiral defect depth can be reduced by means of taking such actions as changing the reduction zone of the Assel mill’s roll profile into a multi-section line，getting the rolling zone optimized as a dual-curve design，and setting the mill’s inlet cone as 1.5°. As a result，the wall thickness accuracy of the Φ219 mm×8 mm steel tube for accumulator service has been enhanced up to±8%.