Abstract: High-precision ultrasonic velocity measurement is of great significance for characterizing the thermal expansion of ultra-low expansion glasses, and the key to ultrasonic velocity measurement problem is the time of flight (TOF) estimation. Aiming at the problem that the TOF measurement accuracy is low and the repeatability error of the ultrasonic velocity measurement is large, a method based on the correlation principle in signal processing is proposed to measure the ultrasonic velocity, and a simulation is carried out with MATLAB to verify the feasibility. This method is based on the obvious relationship between the primary and secondary bottom waves of the tested sample. After filtering and de-noising the two consecutive bottom waves, the correlation is calculated to determine the TOF of the ultrasonic waves in the tested sample. The correlation method is used to investigate the ultrasonic velocity of ultra-low expansion glasses, and the results show that the relative error between the ultrasonic velocity measured by the correlation method and that measured by the typical peak method does not exceed 0.012%, the repeatability error is 0.1 m·s^-1. The correlation method is therefore feasible and reliable for ultrasonic velocity measurement and has great potential for nondestructive characterization of the thermal expansion uniformity of large ultra-low expansion glasses.