Abstract: This paper deduces the relatioship between concerntration of binary gas and the ultrasonic transit time and temperature by Ultrasonic transit physics action in binary gas.It is the theoretical basis for ultrasonic measurement concentration of binary gas.The paper introduces the structure of the ultrasonic measurement experiment principle and experiment results of ultrasonic transit characteristics.The paper measures the concentation of the chlorine and air in the experiment.Experimental results Show that concentration error is less than ±0.5%.