Abstract: The straightening process is generally used to eliminate the lengthwise curves and the roundness errors of oil casings after their rolling and heat treatment.The straightening process as the last procedure in the production of oil pipes will determine their geometrical sizes and influence their mechanical properties.The relations between the straightening amount and the residual stress are researched in order to meet the requirements for the straightness and the roundness of oil casings.The deformation laws during their straightening are analyzed.The finite element model for the straightening of oil casings is established.