In this paper, the numerical-experimental method has been developed to study the pyroplastic deformation of hard porcelain ceramic body during liquid phase sintering process. The pyroplastic deformation mainly depends on the rheological and thermal properties of the ceramic materials. In order to study these properties experimentally, the raw materials of standard hard porcelain mixture as a ceramic body were designed and prepared. For modeling, the finite element method is implemented in the CREEP user subroutine code in ABAQUS for the ceramic specimens during the liquid phase sintering process. Densification results confirmed that the bulk viscosity was well-defined with relative density. It has been shown that the shrinkage along the normal axis of slip casting is about 1.5 times larger than that of the casting direction. The stress analysis proved that the sintering stress is more than the hydrostatic stress during the entire sintering time so, the sintering process occurs completely. Dilatometry, SEM, XRD investigations as well as bulk viscosity simulation results confirmed that the “mullitisation plateau” was presented as a very little expansion at the final sintering stage, because of the highly amount of mullite formation.