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In order to improve the distance measuring precision, a distance measuring and data processing system based on AVR microcontroller is constructed. The ultrasonic distance measuring principle is analyzed, using AVR microcontroller as processor, some circuits are designed including ultrasonic generating and transmitting circuit, ultrasonic receiver and signal processing circuit, temperature measuring and compensating circuit, and so on. In view of the influence of temperature on ultrasonic velocity, according to the relationship of ultrasonic velocity and temperature, the ultrasonic velocity compensating algorithm is designed. In order to increase the echo time measuring accuracy, and decrease the interference of random noise and the other spurious noise from the air, the mean value digital filter method is put forward to deal with the counting time. The measured results show that within the scope of 3cm to 400cm, the measure data is accuracy using the ultrasonic distance measuring system, the most error is 0.66cm.