Carbon Nanotubes /AZ31 alloy composites were fabricated by joining preform of CNTs during melting under the protection of Ar. Composites were prepared by means of equal channel angular pressing ( ECAP) by Bc route in the die with the intersecting angle of 90°. Effects of the pressing passes on the microstructure and the mechanical properties of composites during ECAP were investigated; The fractographs were observed and analyzed via scanning electron microscope (SEM). The results indicate that a great deal of ultra-fine grains appear in CNTs/AZ31 Alloy Composites just after one pass of ECAP; With the increase of pass number, the proportion of ultra-fine grain increases. With 4 pressing passes, the grains are effectively refined to a mean size of 2 μm. And with increasing in the pressing passes, elongation of the composites is increased and the tensile strength is decreased as a result of the refinement of grain size. CNTs were broken under high shearing stress, and the particle distribution in the matrix alloy was homogeneous.