The deformation behavior of equal channel angular pressing (ECAP) was discussed by using plasticity method. The node mapping method is employed to realize the analysis of multi-pass ECAP by using three-dimensional FEM methods for pure aluminum. The single-pass ECAP is a non-uniform shear deformation process in the cross-section of the workpiece. The uniform deformation processing routes are obtained during multi-pass ECAP process. In addition, the density of dislocations and defects of crystal lattice are also largely changed for different processing routes. The grain microstructure is gradually refined with the increase of the pressing passes. The grains and their distribution obtained by route Bc are more useful for producing the material with high angle grain boundaries. The grain microstructure of the cross section of the pressed material decreases with the increase of strain, and some grains exhibit transformed grain boundary (PTB) fringes. The dislocation density in the grain decreases, and the grain boundary presents equiaxed distribution.