Abstract: To establish a relationship between wave velocities in concrete pile shaft measured respectively by the ultrasonic wave method and low-strain reflected wave method,a simplified formula for the ratio of wave velocity in infinite medium to that in one dimensional bar was proposed herein by use of the Kelvin-Voigt viscoelastic theory.It was shown by theoretical and experimental studies that the ratio of ultrasonic wave velocity to 1.054 times of low-strain reflected wave velocity ranged among 1.03～1.12,which decreased with increasing of the age,Young’s modulus and strength of concrete.