The relationships between flow stress curve and microstructure evolution in strain induced dynamic phase transformation (SIDT) of low carbon steel (0.22wt.%) were quantitatively investigated. The deformation was carried out at just above Ar3 temperature (710°C) as a function of strain rate (0.01-5/sec). The softening process of SIDT was well agreed with calculated result derived from Avrami’s and constitutive equation at higher strain rate than 0.5/sec. However, the calculated results differed from the experimental curve at strain rate of less than 0.2/sec. This is due to fact that the dynamic transformation from austenite to ferrite can not be completed owing to less stored energy during hot deformation.