Abstract: A high-sensitivity air-coupled ultrasonic transducer with an acoustic matching layer based on epoxy resin/hollow glass microsphere (HGM) is investigated. In order to improve the dispersion of low-density HGM in high-density epoxy resin matrix, poly(methyl vinyl ether-alt-maleic anhydride) (PVMMA) was grafted onto the HGM surface (PVMMA-g-HGM). The morphology and surface chemical characteristics of modified HGM and HGM/epoxy resin composite were analyzed. An air-coupled ultrasonic transducer was fabricated with the improved matching layer, which achieved a peak-to-peak voltage of 4.88 V. In addition, the gas ultrasonic flowmeter equipped with the improved ultrasonic transducer had better flow field adaptability, and the relative error was less than 1.0%. This work is to propose a new technology to improve the performance of ultrasonic transducer in gas ultrasonic flowmeter.