Based on the nonequilibrium thermodynamic theory,a new thermo-viscoelastic relation at finite strain is proposed.Under the assumption that the specific heat at a fixed strain and fixed internal variables can be regarded as a constant,a new expression for the free energy which decouples the mechanical and the thermal effects is derived.Through an analysis of the mesoscopic deformation mechanism of solid polymers,a set of internal variables is introduced,and an internal-variable constitutive theory in thermo-viscoelasticity at finite strain is formulated.An explicit expression of a thermo-viscoelastic constitutive relation is obtained for solid polymers in the case where their molecular network has a randomly oriented distribution function at reference configuration.Moreover,the relationship between the relaxation time and the temperature is also discussed.The viscoelastic constitutive theory proposed in reference is only a linear approximation of the present theory.