精准的声速测量对于表征超低膨胀玻璃的热膨胀特性具有重要意义，高精度的渡越时间（TOF）估计是使用时差法进行声速测量的关键。针对TOF测量精度不高导致声速测量重复性误差大的问题，提出了一种利用信号处理中的相关性原理来测量声速的方法，并用MATLAB软件进行了仿真以验证该方法的可行性。该方法利用被测试样的一次底波与二次底波具有明显关系的性质，对两次底波进行滤波去噪后计算其相关性，确定超声波在试样中的TOF。利用相关法测量了超低膨胀玻璃的声速。结果表明，相关法测得的声速与典型的峰值法测得的声速相对误差不超过0.012%，且声速测量的重复性误差小于0.1 m·s^-1。因此，相关法测量超低膨胀玻璃的声速是可行且可靠的，其具有无损表征大尺寸超低膨胀玻璃热膨胀均匀性的巨大潜力。

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.