Abstract: The constitutive model of steel under monotonic loading is the basis for structure analysis. In order to calculate the response of high-strength steel structures and to analyze the member behaviour more accurately and to give some references to engineers when applying high-strength steel, this paper updated the parameters of the multi-linear constitutive model of high-strength steel and presented a nonlinear constitutive model based on the Ramberg-Osgood model by means of summarizing the experiment results and by carrying out lots of tensile tests. It has been proved that a nonlinear constitutive model could simulate the stress-strain relationship of high-strength steel under monotonic loading well by comparison with the experiment data. Moreover, to give a consideration to both accuracy and efficiency, a revised multi-linear constitutive model is proposed, which could present the nonlinear material property of high-strength steel and show the similarity in the meantime.