The invention discloses a brake pedal system with the adjustable pretightening force, and belongs to the technical field of automobile brake devices. The brake pedal system with the adjustable pretightening force comprises a pedal, a torsion spring, a worm gear, a worm and a driving device. A transmission shaft is arranged on the upper portion of the pedal and is connected with a brake system of an automobile; the driving device is connected with the worm which is connected with the worm gear; and the torsion spring is arranged between the worm gear and the pedal. The brake pedal system with the adjustable pretightening force comprises the pedal, the driving device, the worm, a nut and a compression spring. The transmission shaft is arranged on the upper portion of the pedal and is connected with the brake system of the automobile; the driving device is connected with the worm, and the nut is in screwed connection with the end of the worm; and the nut is connected with the pedal through the compression spring. According to the brake pedal system, in the driving process, the foot of a driver can be stepped on the pedal all the time, the automobile is braked in time when the emergent condition happens, and the driver cannot step on an accelerator by mistake.