The determination of the acoustic properties is important in the field of underwater acoustics. We proposed a new method of determining sound velocity and attenuation constant of sediments, by measuring the frequency and the resistance at the electrical terminals of a resonating piezo-electric transducer, which is placed at the inner, top of an acoustic tube vertically inserted into the sediment, that is, an open acoustic tube method. In this method, it is needed to measure the resonant frequency and the resonant resistance of the loaded transducer, and the resonant frequency, the resonant resistance and the quality factor of the unloaded transducer. This paper studies on fast measurements of the resonant characteristics by using pulse response method. The motional admittance of the transducer is calculated by using Fourier transformation of the input pulse voltage and the motional current of the transducer. From this discrete motional characteristics, the accurate resonant frequency, resonant resistance and quality factor are obtained by using least squares approximation method. The experimental results show the usefulness of the present method.