The superplastic tensile tests of burnresistant WSTi3515S alloy with large grains were conducted on electronic universal testing machine.The effect of thermodynamic parameters on superplastic properties and mechanical behavior was analyzed,and the superplastic constitutive equation of the alloy was established.The results show that WSTi3515S alloy has superplasticity in a wide temperature and strain rate range ie.800~920 ℃ and 0.000 5~0.01 s-1 respectively with the maximum elongation of 556% at high temperature and low strain rate.Different from finegrained superplasticity,the steady state deformation stage in the true stressstrain curves during the superplastic tensile tests is very short or even absent.The deformation is mainly concentrated in the quasisteady state deformation stage.Moreover,the longer the quasi steady state deformation stage,the larger elongation is obtained.The constitutive equation of WSTi3515S alloy is constructed by Arrhenius equation and stepwise regression respectively.Error analysis shows that the constitutive equation constructed by the stepwise regression has a good accuracy,and the error value is less than 5%.