Al-Mg series alloy plays an important role in offshore manufacturing, transportation and aerospace industries for its high strength-to-weight ratio, high corrosion resistance and good welding performance. For high magnesium Al-Mg alloy, β phase always acts as a restraint condition to the whole thermal mechanical processing (TMP) procedure. Its positive effect is still unclear. In this work, the effect of coarse β(Al₃Mg₂) phase of Al-10Mg alloy annealed at 573 K for 24 h and applied double passes uniaxial compression on microstructure evolution was studied by using OM, XRD, EPMA and EBSD. The result shows that discrete coarse β phase was precipitated in the interior of grains after 573 K and 24 h annealing treatment. The true stress-true strain curve of annealed sample was lower than that of solution treated one. Hardening rate of annealed sample was lower in first compression pass, and conversely higher than that of solution treated one in the second pass. Solution Mg atoms play an important role in strain hardening during dynamic recovery. Dislocation slipping was obstructed by coarse β phase, and then low angle boundary (LAB) was stimulated near coarse β phase. Not just bulging nucleation mechanism working, dynamic recrystallization nucleation was stimulated and microstructure was refined. Since part of deformation-stored energy was lured away by LAB, lattice rotation of deformed grains were weakened possessing {001} and {101} textures simultaneously. Schmid factors of three blocks with different lattice orientations were calculated, which suggested that alloy can load more plastic deformation after annealing treatment. Texture of recrystallized new grains was weakened at the same time. Microstructure anisotropy could be controlled by coarse β phase in TMP.