Equal channel angular extrusion (ECAE) is a technology of refining crystal grain. In this paper, ECAE was introduced into the preparation of semi-solid billet and the extrusion process was simulated using finite element method. The variation of stress (mean stress, max principle stress, effective stress), the distribution of strain, the lattice change were obtained. The results show that not only does the shear stress exist, but also the normal stress in the extrusion process; the stresses in die inner corner of channel and outer corner of channel are not the same. In the inner corner, besides the simple shear, there are compression, and in the outer corner, tension. The strain is non-homogeneous and appears a graded distribution.