Abstract: As-extruded AZ31, AZ61 and AZ91 alloys were prepared. The effects of second phase volume fraction and the microstructure uniformity on the properties of as-extruded AZ magnesium alloys were investigated by optical microscopy,scanning electron microscopy and tensile test at room temperature, etc. The results indicate that as-extruded AZ31, AZ61 and AZ91 alloys are composed of α-Mg matrix and β-Mg₁₇Al₁₂phase. With the increase of Al content, the grain size decreases and the second-phase volume fraction increases, changing from dispersive granular distribution to the strip distribution parallel to the extrusion direction and chain-like distribution along the grain boundary. The yield strength gradually decreases from 224.89 MPa to 182.78 MPa due to the combined effect of second phase and texture weakening more than the effect of fine grain strengthening. The tensile strength increases significantly from 279.29 MPa to 356.22 MPa due to fine grain strengthening and pinning effect of the second phase, and the elongation increases from 8.81% to 18.27% due to the fine grain strengthening and improves grain uniformity.