Abstract: This paper mainly focused on the strain-displacement relationship（ε-d） during tensile test for establishing the relationship among the force/stress,strain and displacement.Several materials were tested on MTS 810 hydraulic servo-machine,and the experimental data was analyzed.The results showed that the ε-d was a linear function during elastic stage,while it indicated nonlinear in the whole plastic stage,so it was unreliable to determine the yielding strength by the displacement method.The ε-d dependence was in good conformity with polynomial function by fitting the measured data of strain in the range of extensometer（up to 32% at RT and 16% at HT of the elongation） and the whole displacement,and the ε-d values could be obtained up to 70%（RT） or 35%（HT） of the elongation by extrapolating the above function and related data,while the maximum fitting error was no more than 3%.That is to say,as the result of overcoming the limit range of extensometer,we can perfectly get the complete engineering stress-strain（σ-ε） data.