Abstract: Through systematically analysing the dynamicstrain aging behaviour and the testing data of structural steel DH-36, theconstitutive model of the third-type dynamic strain aging has beendeveloped. Then based on thermal-activated physical concept constitutivemodel and the combinatorial principle of plastic flow stress, a unifiedconstitutive model is finally obtained with the description for thethird-type dynamic strain aging. This model not only can describe thethird-type dynamic strain aging phenomenon, but also the mechanicalbehaviour of DH-36 steel in a wide range of temperatures(77~1000K) and strain rates(0.001~3000s^-1). There is a good agreementbetween theoretical predictions and experimental results.