The formulation of a new mathematical model of deformed viscoelastic composite is shown in the work. The method of constructing a model is based on commonality problems of determining the effective modules of inhomogeneous elastic composites and viscoelastic bodies, which demonstrate the dependence of the mechanical properties from the duration of load action. Mathematical model of hybrid efficient modules has been constructed on the superposition of expressions for known effective modules of Voigt and Reuss, Hashin and Shtrikman. The new model summarizes the properties of classical approximate approaches. We have shown that the calculations of stress-strain state with the help of new effective characteristics provide a more accurate prediction in comparison with known models.