The invention discloses a brake system device capable of preventing stepping on an accelerator pedal by mistake. The brake system device comprises a pressure sensor arranged on a left foot rest pedal of an automobile; the pressure sensor is connected with an oil supply system and a brake system of the automobile; the pressure sensor is provided with a preset pressure value; the pressure sensor only can be started when being subjected to a pressure value exceeding the preset pressure value; if a driver adopts the accelerator pedal as the brake pedal by the right foot by mistake, the driver consciously uses the left foot to forcibly step the left foot rest pedal, the pressure sensor is started when sensing the pressure value exceeding the preset pressure value, a danger signal is transmitted to the automobile oil supply system and the automobile brake system quickly, and the automobile turns off an engine quickly and performs emergency brake, so that a double-safety device, by which the automobile can turn off the power provided by the engine quickly and adopt emergency brake under the condition that the accelerator pedal is stepped by mistake, is achieved, and traffic accidents are avoided effectively.