The invention relates to an automatic steel rotation method for medium plates, which belongs to the technical field of steel rolling. The method comprises the following steps of: 1, performing acquisition on a plate blank image; 2, performing edge detection on the plate blank image; 3, performing image distortion and calibration processing; 4, performing image binarization; 5, performing plate blank boundary tracking to obtain a boundary point set; 6, performing linear detection on plate blank boundary and calculating an rotating angle of a plate blank; 7, driving a steel rotation conical roller bed for steel rotation; 8, performing judgment of steel rotation in-place; 9, performing processing of steel rotation timeout; and 10, performing processing of steel rotation completion. The method has the advantages that the method has simple equipment installation and quick detection speed, can execute one-time detection and control within 100 ms, is based on an industrial Ethernet interface and basic automation communication, has stable and reliable steel rotation process, and is suitable to be embedded into an automatic steel rolling system of the medium plates for application.