Based on Kolmgorov-Johnson-Mehl-Avrami analysis, a new bainite kinetics of high strength low alloy steel in fast cooling process was developed by utilizing different experimental methods.Upper bainite transformation morphological evolutions at a cooling rate of 8.3 K/s were directly observed by laser scan-ning confocal microscopy.This qualitative analysis suggests that bainite packet is more suitable to give a one-dimensional growth model if it is considered as a transformation unit.The nucleation rate of bainite packets in fast cooling process is assumed to give an a priori item.One-dimensional growth model with constant growth rate which is assumed as a function of cooling rate is adopted as well.Thus, the devel-oped new bainite kinetics is simple in expression and contains an adjustable parameter and an empirical pa-rameter.Experimental results show upper bainite and lower bainite transformations in fast cooling proces-ses.Their referential phase volume fractions are calculated by the expanded lever rule on the first deriva-tive dilatometer curves.For the similar transformation mechanisms, upper bainite and lower bainite are considered to give the same kinetics.With considering the Nakamura′s equation, the bainite kinetics is fit-ted with experimental data.Results show that bainite volume fractions and bainite transformation rates can be expressed precisely by the newly developed bainite kinetics.