In this paper,the AZ80 magnesium alloy billets of size of 100mm×50mm×170mm was extruded by CEEOP.The effect of 1~4 pass deformation of CEEOP to the equivalent strain、 microstructure and mechanical properties of AZ80 magnesium alloy through simulation、OM、tensile test and hardness test.The results show that with the increasing of CEEOP pass,the grain size was more small and uniform;the grain size could be defined from 200μm to 6μm after one-pass;after four-pass, the size of equal-axial grain was reduced to approximately 1.5μm and the distribution was uniform,furthermore,the mechanism of grain refinement is mechanical fragmentation and dynamic recrystallization;the grain refinement effect was not obvious after two-pass.The mechanical properties have been greatly improved compared with the annealed alloy. One-pass deformation of CEEOP can significantly improve the hardness of annealed alloy from 61.5HB to 83.07HB.Similarly,four-pass deformaion can also obviously improve that from 61.5HB to 86.27HB.The ultimate tensile strength and yield strength via one-pass can improve from 230.9MPa ,115MPa to 262.7MPa ,155MPa ,respectively.And after four-pass,they would increas to 294MPa ,170MPa,respectively. Compared with the microstructure and mechanical properties of ECAP,at the same deformation temperature and strain accumulation,CEEOP can better refine grain and improve the tensile strength and yield strength of the material.