A solution of the problem under consideration is important in the optimization of a technology of production and composition of high-temperature superconductors. We suppose a criterion of plasticity and a related law of plastic flow that may describe both the motion in the body of a specimen and the process of consolidation of powder under the compressing. First, adding the first invariant of the stress tensor into the criterion of plasticity and a related law of plastic flow, we consider the effect of volume change on the process of deformation of the powder under compression. Then, we discuss the application of non-associated laws of plastic flows to the process of high-temperature super-conducting powders. Finally, involving the rule of dilatation and considering the dissipation due to rearrangement of particles of the powder and friction of these particles, we present a criterion of plasticity and a related law of plastic flow.