Plastic flow and the evolution of distribution of the components of stress tensor in a sample under compression and shear in rotational diamond anvil cell are studied using the finite-element method(FEM).Pressure self-multiplication effect is revealed during rotation of an anvil after compression below critical force. Significant heterogeneity of accumulated plastic strain (especially near contact surface with diamond) is found. The obtained results are important for determination and interpretation of kinetics of strain-induced phase transformations (PTs) and chemical reactions.