When the vehicle driving, ranging probe constantly monitors the distance from the front vehicle, and according to the speed, the relative speed in accordance with the established mathematical models and control algorithms calculate whether the vehicle is in safe driving condition. If the distance between vehicles is too near ,the system will immediately alarm to remind artificial deceleration. If the manual is not enough time to brake, as a remedy, the system firstly pumps to remind deceleration. If the danger is still there, the system will continuously hit the brakes until the danger disappears.The system consists of ranging probe, warning  host ,tandem controller and brake motor.