Three deformation stages of straightening T-rail’s warpage, including elastic deformation, elastic-plastic deformation and elastic unloading springback, were analyzed according to the elastic-plastic mechanics theory, the load-stroke expressions of three deformation stages were gained through deriving relationships among load, bending moment and stroke, and then the straightening load-stroke model was established. By using the model, the straightening stroke could be calculated directly and accurately according to the initial deflection. In order to verify the model presented, taking T89/B guide rail for example, the straightening experiment was conducted. Comparing the calculation strokes by model with experimental results, the relative errors are less than 10%. It showed the presented model was practical. It will give theoretical support to the development of automatic machines for T-rail’s warpage straightening.