A circuit design of ultrasound guiding system is introduced. The system has one ultrasonic emitter and three sensors. These sensors are located at different apex of an equilateral triangle. The emitter is arranged at center of the equilateral triangle. With the emitter and the sensors, obstacles in front of the blind can be detected by using time-of-flight of the ultrasonic wave. Because amplitude recession, temperature and humidity may influence the measurement accuracy, a small area of 20 to 140 centimeters in front of the sensors has been considered and evaluated. Some experiment results and conclusions are also given in this thesis.