Ultrasonic ranging is robot obstacle avoidance methods, but when multiple ultrasonic ranging system used at the same time easy to produce crosstalk problems. Apply pseudo random code m sequence in the ultrasonic ranging system, each for launch ultrasonic encode all the way, make the ultrasonic wave can be emitted by transmitting terminal identification. The launch of the ultrasonic echo of coding and local autocorrelation arithmetic coding, using msequence good autocorrelation characteristic, judge the echo is effective echoes or interference. System can effectively identify the clutter echo and abandon it, so as to avoid occur crosstalk between multiple ultrasonic ranging system. The experimental results show that the system of ranging error is less than 1.9%.