The extrusion deformation behavior of Mg-3Bi and Mg-6Bi alloys at 400 ℃ and a strain rate of 0.001 s-1 was investigated, and the microstructure characteristics during extrusion were analyzed. Results indicate that as the Bi content increases from 3% to 6%, the plasticity of the alloy improves, the elongation increases from 2.1% to 5.6%, while the tensile strength increases from 188.2 MPa to 209.2 MPa. Under high temperature extrusion deformation, the dominant softening mechanism of the Mg-3Bi alloy is discontinuous dynamic recrystallization(DDRX), whereas that of the Mg-6Bi alloy involves both DDRX and particle-stimulated nucleation (PSN) in this process, the grain size resulting from DDRX is larger than that of PSN. When Mg-Bi alloys are extruded through the die, the strain in the edge region of the die is singificantly greater than that in the central region, forming a deformation texture similar to that of Equal-Channel Angular Pressing(ECAP) and prone to forming a bimodal structure. Once the accumulated strain reaches a critical value, PSN is initiated. After extrusion deformation, the grains in both the edge and central regions of the die exhibit a high degree of recrystallization, presenting a typical extrusion fiber texture. This texture arises from DDRX, PSN, and Zener pinning effect of the second phase. The ranked contributions to the improvement of the mechanical properties of Mg-Bi alloy from highest to lowest, are grain refinement, dislocation strengthening and nano-phase strengthening mechanisms. Compared with the Mg-3Bi phase, the dimple density of Mg-6Bi is higher, which disperses stress concentration and consequently enhances plasticity.