Abstract: In this study, the continuous extrusion is combined with an equal-channel die. The microstructure evolution of Al-Sr master alloy under large strain extrusion is analyzed by finite-element simulation, metallographic microscopy, X-ray diffraction, and transmission electron microscopy. Results show that the maximum effective strain in the equal-channel die can reach 16, which appears on the a-path passing through the outer corner of the first die angle, and the refinement effect of Al4Sr phase is the best. The refinement effect of each path on Al4Sr phase is as follows: inner a-path > middle b- path > outside c-path. Using the extrusion method with one die of double hole, the coarse Al4Sr phase particles in the center of cavity inlet can pass through the a-path with largest strain in the equal-channel die, so that they can be effectively refined. Finally the particles of Al4Sr phase in the center and edge of the product are effectively refined, with an average length of about 4.5 μm. Transmission electron microscopy observation shows that after large plastic deformation, due to the increased cumulative strain and increased microscopic strain, the internal dislocations of Al4Sr phase are entangled and delivered, forming a dislocation wall that interacts with the external dislocations to break Al4Sr phase particles. The fragmentation exerts a significant refining effect on Al4Sr phase particles. At the same time, due to the increased interfacial energy, a small amount of Al4Sr phase dissolves.