By the severe plastic deformation, the equal channel angular pressing method (ECAP) has been used for producing metal materials with the ultra-fine grain size and specific mechanical properties, in particular high yield strength. Analytical approaches have also been studied by few researchers. However, none of the previous analyses have taken into account the strain hardening of the material by considering the microstructure evolution. In this paper, the deformation behavior and the strain harden of aluminum during equal channel angular pressing was calculated on the basis of a dislocation evolution model. Then simulated stress, strain and strain distribution and strain hardening were analyzed. The strain is seen to rapidly increase when the material passes the shear area. This makes a maximum value of stress. And for the congregation of dislocation density, the maximal value of strain increase with the process continuing.