Abstract: The accuracy of mine ultrasonic gas flowmeter needs to be improved. The cross-correlation detection signal has 'signal hopping' phenomenon and affects the measurement precision of ultrasonic transit time. In order to solve the above problems, this paper proposes an automatic tracking method of reference waveform of mine ultrasonic gas flowmeter. While calculating the ultrasonic transit time, the cross-correlation operation is carried out between the ultrasonic reference waveform and the real-time received signal waveform. The reliability of the cross-correlation detection is calculated. The reliability effective threshold value and the reference waveform update threshold value are set. The reliability of the cross-correlation coefficient is evaluated so as to determine whether the reference waveform is updated. When the reliability is less than the effective threshold, it is determined that the received signal is invalid, and the ultrasonic signal is re-sent. When the reliability is greater than the update threshold, it is determined that the received signal waveform is highly consistent with the reference waveform. There is no need to update the reference waveform. When the reliability is between the effective threshold and the update threshold, it is determined that the received signal is valid. And the original reference waveform is replaced with the current received signal waveform to realize automatic tracking of the reference waveform. This paper analyzes the two kinds of waveform changes of ultrasonic received signal which may cause ultrasonic transit time error of one waveform period. The waveform changes are continuous envelope deformation and instantaneous envelope distortion. The change of gas flow rate, temperature and pressure will lead to the continuous change of received signal envelope. Spike pulses, random signals and periodic interference may cause instantaneous envelope distortion of the ultrasonic received signal. The instantaneous envelope distortion can be divided into three cases, severe distortion of the main peak, slight distortion of the main peak and non-main peak distortion. The experimental results show that under the influence of different flow velocity, temperature, pressure and noise, the relative error of ultrasonic gas flowmeter is less than ±1.0%. The results meet the measurement requirement of precision level 1.0. The automatic tracking method of reference waveform provides a guarantee for the accuracy and reliability of flow measurement.