Although a lot of effort is being spent on understanding the mechanism of amorphization and predicting alloy compositions that possessed high glass forming ability (GFA), the efficient and effective method has yet to be developed.Generally, it has been widely accepted that glass formation is essentially retaining the liquid structure as well as avoiding the crystallization.In this paper, a modified phase field method (PFM) is proposed for quantitative simulation of the glass transition and the competition between crystalline phase and amorphous phase during the rapid solidification process in Fe-B binary alloys.The influence of different cooling rate on the competition between crystalline phase and amorphous phase are analyzed and the lowest rate that the crystallization onset is observed is estimated as the critical cooling rate (Rc).