Stress-dependence of the intrinsic time of viscoelastic materials is investigated.The influenceof stress level on the intrinsic time is considered to be similar to that of lemperature,pressure,solvent con-centration,damage and physical aging.The time-lemperature-stress equivalence principle is proposed,byemploying which,the creep curves at different temperatures and stress levels can be shifted into a mastercurve at reference temperature and stress level.Thus the long-term creep behavior of viscoelastic materials ata lower temperature and stress can be predicted from the short-term one at a higher temperature and stress.As an example,the nonlinear creep behavior of high-density polyethylene(HDPE)at room temperature isstudied using the time-temperature-stress equivalence principle presented. Stress-dependence of the intrinsic time of viscoelastic materials is investigated. The influenceof stress level on the intrinsic time is considered to be similar to that of lemperature, pressure, solvent con-centration, damage and physical aging. The time-lemperature-stress equivalence principle is proposed, byemploying which, the creep curves at different temperatures and stress levels can be shifted into a mastercurve at reference temperature and stress level.Thus the long-term creep behavior of viscoelastic materials ata lower temperature and stress can be predicted from the short -term one at a higher temperature and stress. As an example, the nonlinear creep behavior of high-density polyethylene (HDPE) at room temperature is constructed using the time-temperature-stress equivalence principle presented.