This research aims to estimate properly stress of ceramics during sintering process with simulation. Comparing some conventional models which have been proposed to predict deformation, we would like to consider following three aspects in the simulation model for stress estimation; (a) modeling based on finite deformation theory to solve heat transfer and force equilibrium equation in deformed geometry, (b) unified modeling independent of temperature history to consider temperature gradient inside bulks, (c) modeling irreversible deformation due to stress with viscoplastic model (not viscoelastic model). In our model, the deformation gradient is multiplicatively decomposed into thermal and mechanical components, and they are further decomposed into reversible and irreversible ones. To define these components, we assume that thermal and mechanical deformation are independent and identify parameters of each model from experiments with/without uniaxial compression load. For the thermal irreversible deformation (sintering deformation), Master Sintering Curve is employed, which means that deformation of bulks with temperature gradient can be exactly represented by unified model. For the mechanical irreversible deformation, Peric’s viscoplasticity model is used to represent creep deformation during sintering process. In this simulation model, it would be shown that temperature gradient during sintering process causes mechanical irreversible deformation, that is, it results in final non-uniform deformation even if overall sintering shrinkage is the same.