The invention discloses a roll breakage protecting control method for a working roll of a heavy and medium plate mill, which comprises the following steps: additionally arranging two pressure sensors at a driving side and an operating side on an AGC control hydraulic valve stand; transmitting detected signals of pressure intensities to a mill control PLC; obtaining the pressures of an AGC cylinder by respectively multiplying the pressure intensities detected by the two pressure sensors by the area of the AGC hydraulic cylinder by the PLC, wherein the pressures of the AGC cylinder are respectively the pressures acting on two sides of the working roll; comparing the calculated two pressures of the two sides of the working roll respectively with force detected by a piezomagnetic head; and when the comparison result is larger than 800T, considering that the working roll of the mill is abnormal currently, immediately stopping the current action, and opening a roll gap quickly to protect the working roll. The invention takes the detected deviation value of actual forces of an upper roll and a lower roll as a controlled object, limits the actions of the upper roll and the lower roll, avoids breakage of the working roll, and can effectively protect the working roll when the mill has abnormal conditions, thereby preventing the roll breakage.