Abstract: Flow-opening degree calibrating curve is usually used for accelerating the control speed of flow in the ultra fast cooling system of plate mill. The precision of calibrating curve influences directly the accuracy of flow control. Taking the new ultra fast cooling equipment applied in many plate mill plants of iron and steel group corp as an example, the electric valve regulating characteristics was analyzed, and the effective auto-calibrating method of flow-opening degree calibrating curve was developed. The results showed that this method of obtaining flow-opening degree calibrating curve by using flow auto-calibrating technology not only is convenient for maintenance but also achives the better speed and accuracy of flow control. It could be used to improve the design of ultra fast cooling equipment and control system.