Abstract: The static and dynamic continuous cooling transformation (CCT) curves of 440 MPa high-strength IF steel were tested by dilatometer and thermal simulation tester, and the phase transformation law of the steel was analyzed. The results show that ferrite appeared at the start stage of static and dynamic transformation, and bainite ferrite appeared with the increase of cooling rates and the grains of phase transformation product were refined. Comparing with static transformation, dynamic transformation increased the starting temperature of austentite transforming to ferrite, promoted ferrite phase transformation and refined the grains of phase transformation products.