In order to investigate the effect of homogenization annealing on the second phases of Mg-3Al-1Zn-2.2/5Sr magnesium alloys, the type and formation theory of second phases in the as-annealed Mg-3Al-1Zn-2.2/5Sr alloys were investigated by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD) combined with Pandat thermodynamic calculation software. The results indicate that after homogenization annealing at 400 oC for 15 h and cooling in furnace, the fraction volume of Al in (Mg, Al)17Sr2 phase preliminarily formed in the as-cast structure of Mg-3Al-1Zn-2.2/5Sr alloys decreases slightly. In addition, a huge number of granular Al4Sr phases are formed along the edge of the (Mg, Al)17Sr2 phase in Mg-3Al-1Zn-2.2Sr alloy, while the change of (Mg, Al)17Sr2 is hardly to be observed in the microstructure of the alloy with 5% Sr addition.