The invention discloses a device for controlling the safe pressure of a horizontal balance system of a rolling mill. The device comprises an electric control system and a hydraulic execution system connected with the electric control system through a data line, the electric control system comprises a CPU (Central Processing Unit), a PI (Proportional Integral) regulator, a amplitude-limiting generator, an input/output board and a pressure flow conversion module, can calculate corresponding pressure values according to different cascading modes of the rolling mill and then limit the amplitude so as to output minimum balance force. Accordingly, the invention also discloses a method for controlling the safe pressure of the horizontal balance system of the rolling mill. The method is simple and convenient to operate and can ensure the long-term safe and stable operation of the system.