Based on plastic mechanics total strain theory

big diameter thin-walled tube bending forming is researched by assuming that only axial stress and strain in every fiber layer exist during tube bending process. The strain calculation equations of tube bending process are created by assuming the function of neutral layer offset angle and cuneiform angle with the angle coordinate. Then the stresses are gained by the relation of strain and stress

and the contact pressure and friction between die and tube are obtained through the integrating of stress on section and the force equilibrium in differential element. Outside force is calculated through the integrating of inner force on boundary. At last the coefficient of the function of neutral layer offset and cuneiform angle in bending segment are calculated through the force equilibrium equation and energy equilibrium equation. Thereby the springback angle is calculated and the infl uence law some process parameters to springback is analyzed.