Abstract: The steel waveguide rods with 7 different diameters were investigated. The lead-break signals were collected in the center of the end surface and circumferential surface separately. The signals were analyzed for the rods of 10 mm diameter with 2.5 m and 1.0 m length. The effects of signal separation of longitudinal wave, amplitude, rise time, duration and signal strength were analyzed. The features of the rods for the separation of longitudinal wave and their amplitudes of 7 different diameters with different lengths were summarized. A principle of selecting the diameter and length was proposed. A time-domain map of the signals transferred by the waveguide rod was analyzed. The speed of the longitudinal waves and transverse waves of acoustic signals propagating in the waveguide rod was calculated. A method to avoid the signal positioning error caused by the changes of signal speeds was proposed.