The straightener roll should be in contact with the tube or bar in line during the working process. The traditional calculation method using roll-shape curve equation was extremely complex, so this paper presents a new method of determining roll-shape curvature in the condition of the tube or bar contacted with roller in line. By comparison, this calculation method is simple and easy. Moreover, this method guarantees the quality of product with the required accuracy. This method presents a new way in straightener roller design.