In order to study the impact of fulcrum distance on the straightening the minimum fulcrum distance was determined based on the plastic theory according to straightening pressure force in the process of straightening process where there was no indentation. The optimal distance between the fulcrums straightening has been studied by using of bending curvature changes in the bending deflection formula and support the relationship between the dot pitch. Given initial deflection according to bending deflection and bending deflection the amount range of the fulcrum distance can be determined during the pressure straightening. When the rate of bending deflection determined it can obtain the fulcrum distance at the same curvature. The more fulcrums distance the more bending deflection. The minimum fulcrum distance was three times the power growth with the diameter of work piece. The minimum fulcrum distance is inverse proportion to contact area of pressure head. With the pipe wall thickness decreases the minimum distance also reduced.