To raise the response speed of the ultrasonic gas flowmeter system, a new signal processing method of ultrasonic gas flowmeter is proposed according to the maximum difference value of adjacent peak. In order to improve the measurement precision of this signal processing method, a new kind of intermittent excitation method is presented. The intermittent excitation method is adopted to obtain the echo signal with the maximum difference value of adjacent peaks. The relative position of the maximum difference value of adjacent peaks in the echo signal is always the same under different flow rates. During the actual measurement, the position of the maximum difference value of adjacent peaks is utilized to determine the arrival time of the echo signal, and then the ultrasonic propagation times are calculated to obtain the gas flow rate. The intermittent excitation method and the signal processing method based on the maximum difference value of adjacent peaks are realized on the hardware system in real time. The calibration experiments are conducted to verify the effectiveness of the excitation method and the signal processing method.