Abstract: This paper presents the quantitative prediction of the volume fraction of martensitic transformation in a austenitic steel that undergoes a impact loading. The coupling relationship between strain, stress, strain rate, transformation rate and transformed fraction was derived from the OTC model and modified B-P equations, where the impact process was considered as an adiabatic and no entropy-increased process (pressure≤20 GPa). One-dimensional results were obtained on 304 stainless steel under Hopkinson impact, which agree well with various experimental results.