The invention provides a method and a device for preventing strip steel from deflecting. The method comprises the steps of receiving convexity values of a turning roll and a sink roll in a roll system at a cleaning section; decreasing the cylinder deflection rectification amount of the roll system according to the convexity values; and receiving a preset tension value, and guaranteeing a wrap angle of the strip steel and the roll system at the cleaning section to be in a stable state according to the tension value, wherein the turning roll and the sink roll are double-helix rolls. According to the method, through optimizing convexity and surface structures of the sink roll and the turning roll, introducing tension velocity factor, and establishing a virtuous alkali liquor circle system at the cleaning section, the technical problem that the high-speed running strip steel deflects at the cleaning section is solved.