This paper studies the validity of using impact-echo method to test the dynamic modulus of elasticity of concrete for standard prismatic specimens. It is found that the P-wave speed in a standard prism obtained from the impact-echo test well corresponds to the theoretical one-dimensional P-wave speed, and the dynamic elastic modulus obtained from the impact-echo method are essentially equal to those from the conventional transverse resonant frequency method. This paper adopts impact-echo method to detect the variation of P wave velocities of concrete specimen with the increase of freezing and thawing cycles, which is compared with the variation of fundamental vibration frequencies, thus to conduct parallel evaluation of the decline of relative dynamic elastic modulus using these two methods. The experimental results and theoretical analysis show that using impact echo method to detect the frost resistance of hydraulic concrete is feasible and can be used for durability assessment of hydraulic concrete.