By analyzing the simulation results for stress relaxation with Chaboche model, the effect of loading history is discussed. It is revealed that the Chaboche model without static recovery term cannot demonstrate the influence of prior loading strain rates for drop stress during strain holding period. A modified model based on the Chaboche unified viscoplasticity theory is proposed to mainly focus on the remarkable features of the relaxation behavior of materials. Several numerical examples are discussed, in detail to show some potential descriptions and the strong dependence on prior uploading strain rates for relaxation. The experiments of two materials Type 304 stainless steel and TIMETAL 21S are selected to verify the feasibility of proposed model. A series of consistent simulation and prediction results are obtained, including the dependence of drop stress on various prior loading strain rates, the effect of different peak stresses or holding strains with the same prior loading strain rate, multi-relaxation with relaxation histories, and cyclic plasticity. Finally, the principle of parameter determination is also discussed. (C) 2017 Elsevier Ltd. All rights reserved.