Poisson's ratio plays a significant role in the structural response of solid propellants, which is, in essence, a nearly incompressible viscoelastic material. Numerical models that assume a constant Poisson's ratio generally cannot achieve good results, thus requiring an accurate knowledge of time-dependent viscoelastic Poisson's ratio of solid propellants. In this work, accurate determination of tensile strains and viscoelastic Poisson's ratio of solid propellants using an accuracy-enhanced 2D digital image correlation (DIC) technique is described. To achieve high-accuracy measurement, great improvements were made to regular 2D-DIC technique to maximally eliminate the errors caused by non-ideal loading conditions, specimen deformation and lens distortion. Rigid body translation tests with zero strain state are first performed to verify the accuracy of the proposed DIC technique. Then application of the proposed technique for determining the time-varying viscoelastic Poisson's ratios of solid propellants in stress relaxation tests are demonstrated. The results reveal that, by adequately eliminating the measurement errors associated with the unavoidable out-of-plane displacements and lens distortion, the present DIC technique can be used for precise determination of viscoelastic Poisson's ratio of solid propellants, which is found to be increasing nonlinearly to the incompressible value of 0.50 as time increases.