This article discusses the viscoelastic relaxation properties of bulk cross-linked polymers. The simple dynamic model of a “mesh-like” polymer network is considered for the description of the behavior of bulk cross-linked polymers at stretching. This dynamic network model directly takes into account the following features of bulk polymers: (1) the existence of a fixed average volume of the polymer network, (2) the interconnection between the gradient of the effective viscous medium and the macroscopic deformation of the bulk polymer sample, and (3) the presence of mutual interchain friction. The low-frequency network dynamics determined by the motions with scales greater than the distance between the network junctions is mostly studied. The simplified “coarse-grained” cubic network model is used. The total stress which arises in bulk cross-linked polymers and the viscoelastic functions (the dynamic modulus and viscosity) are calculated. The influence of the interchain friction and of the fixed average volume of the network on the total stress and on the dynamic modulus and viscosity is discussed. The results obtained are compared with the results of the theoretical approaches developed earlier.