According to the present experiment results about the transformation from β－AlFeSi to α－Al(FeMn)Si phase in Al－Mg－Si series alloys, the model and kinetics of phase transformation,and microstructure evolution at 555 ℃ were systematically investigated. The results show that, the homogeneous temperature T can give a significant effect on the transformation kinetics, and with increasing T, the transformation rate increases fast. The nucleus radius of α phase only affects the breakthrough time along the thickness direction of β phase. The distance l between twoα phases mainly has an influence on the dissolving of rim for β phase. The thickness of β phase normally has a greatest influence on the phase transformation β→α,especially for the breakthrough stage of β phase, with increasing the thickness of β phase,the main transformation with longer time in the whole phase transformation process can changes from rim dissolving of β phase to breakthrough along the thickness direction of β phase. The breakthrough time of β phases with the thickness of 0.1, 0.2 and 0.3μm is above 5, 10 and 15 h, respectively, which corresponds with the real experiment results. In addition, if the thickness of β phase is smaller than 0.3μm, the transformation rate f(α) easily reaches above 0.9 after homogeneous heat treatment at 555 ℃ for 16－-24 h. Therefore, the importance of optimizing casting process to make sure the thickness of β phase below 0.3μm, is the same as the homogeneous heat treatment for the better controlling the phase transformation β→α.