An anti-air-return fan system includes a motor, a driving control circuit, and a rotation judgment circuit. The driving control circuit is electrically connected to the motor. The driving control circuit has a driving signal for driving the motor to rotate according to the driving signal. The rotation judgment circuit outputs a judgment signal to the driving control circuit when detecting that the motor reversely rotate. The driving control circuit executes a braking according to the judgment signal. The driving control circuit drives the motor to operate when the rotation judgment circuit detects that the motor doesn't rotate reversely.