Mg alloy has attracted researchers' attention as applied for novel biomedical material because of its super corrosion property and well biocompatibility. Ultra-fine grain (UFG) Mg alloy has certain advantages in the development of medical devices because of its good plasticity and corrosion resistance. Equal channel angular pressing (ECAP) was performed on Mg-3Sn-0.5Mn alloy successfully. The microstructure and grain size were observed and measured by OM and TEM. The mechanical property was tested by microhardness and tensile test, the texture oriented was experimented by XRD, and the corrosion property was tested by electrochemical experiment. After 4 passes ECAP at 320 ℃, the average grain size of Mg-3Sn-0.5Mn alloy reached 1.65 μm, and local grain size reached 0.8 μm. The grain refinement was caused by severe plastic deformation and recrystallization. The elongation increased from 22.2% to 58.6%, the tensile strength decreased from 242.8 MPa to 195.6 MPa after 4 passes deformation. The mechanical tests showed an improvement in the elongation after 4 passes, which were about 3 times higher than in the as-extruded sample, whereas the tensile strength decreased slightly. The texture of Mg-3Sn-0.5Mn alloy changed obviously which contributed to the actuating of the slip system. This change of texture contributed to the improvement of fracture elongation and decrease of tensile strength. The mechanical property of Mg-3Sn-0.5Mn alloy after ECAP was affected by the texture orientation and grain strengthening.