Abstract: The thermal expansion curves of 1000 MPa cold rolled dual phase steel during continuous heating were tested on a DIL805A dilatometer. The volume fraction of austenite in the steel was calculated by the lever rule method, and it is in good agreement with the result of quantitative metallography. The JMAK equation can predict the austenite isochronal transformation kinetics quite well. The influence of cold rolling reduction and heating rate on austenite isochronal transformation kinetics was also investigated. Finally, the equilibrium condition of phase interfaces during transformation was studied by thermodynamic calculation.