Abstract: It is convenient and exact to analyze the bending property (bending moment, curvature and deflation) with real,complex power function stress and strain relationship in the process of rail's straightening. Through the alternately bending test with the same materiel, stress and strain reationship can be found. The mechanical property problem caused by altemately bending of heavy rail can be solved.This method can be used for other steels with different cross section and material.