Abstract: Summarized here in the paper are the four commonly-used mathematical models of stress-strain curve.In light with the power function constitutive equation of the true stress-train curve,the fitting method for the strain hardening exponent n_H with the yield ratio as the parameter are studied.The measured true stress-strain curves of the linepipe as made in two different steel grades are compared with the fitting curves.As a result of the analysis,it is regarded that the sad strain hardening exponent n_H is decreased along with the increase of the yield ratio;and that the Hollomon power function equation as determined by n_H can be used to simply and accurately describing the true tress-strain curve of the high deformationresistant linepipe.