We have formulated the dynamics and the simulation scheme for large deformation of gels using the Stress-Diffusion Coupled Model. Using this model, we have simulated the shrinking process of 2D slab gels undergoing spinodal decomposition, in comparison with the collective diffusion model of gel networks. We reproduced the “plateau period” due to the surface skin formation, and the pattern formations in the inner region of gels by the Stress-Diffusion Coupled Model. ©2000 American Institute of Physics.