If the resonant frequency of the transmitting sensor is 40KHZ piezoelectric ceramic (dual crystal oscillator), the 40KHz high frequency voltage is applied, the piezoelectric ceramic film is based on the high frequency voltage polarity elongation and shorten, then sends the ultrasonic 40KHz frequency, its ultrasonic wave in the form of density spread (the density can be modulated by the control circuit), and transmitted to the wave receiver. The receiver is the use of pressure sensors to use the principle of piezoelectric components of pressure, so that the piezoelectric components of the strain, the emergence of one side is "+" pole, the other side is "-" polar 40KHz sine voltage. Because the high frequency voltage amplitude is small, it must be enlarged. The ultrasonic sensor allows the driver to reverse safely, using the principle of detecting any obstructions on or near the path of the reversing, and issuing a warning promptly. The Designed detection system can simultaneously provide sound and light and Mao's auditory and visual warnings, and its warning indicates that the distance and direction of obstructions in the blind area is detected. In this way, in the narrow place whether it is parking or driving, with the help of reversing obstacle alarm detection system, the driver psychological pressure will be reduced, and can take the necessary action to ease.