Aimed at the problem that the online detection technology of valve packing sealing gas leakage with wide application,low cost and high precision is still lacking,a on-line detection method of valve packing sealing gas leakage was proposed using ultrasonic impedance identification.This method collects the leaked gas of the valve stem and makes it pass into the detection liquid to produce bubbles,counts the bubbles by recognizing the impedance of the bubbles with an ultrasonic sensor,so as to achieve the measurement of gas leakage.The experimental device for bubble floating mechanics based on high-speed camera was built,and the effects of the detection medium,such as water and ionic liquid,on the detection accuracy were investigated systematically.The system of ultrasonic signal acquisition and wireless transmission was designed,the APP program was compiled,and the remote on-line detection of valve packing sealing gas leakage was achieved with the detection error less than 5%.