An coiled optical fiber sensor based on Sagnac interferometer for the measurement of ultrasonic wave propagated on the surface of a solid plate has been proposed and demonstrated. The advantage of this kind sensor is that the feeble vibration produced by ultrasonic wave on the surface of solid plate transmission can be detected accurately. The output optical intensity of interferometer is modulated when the ultrasonic wave signal passes through the sensing coil of the Sagnac interferometer. The amplitude and the frequency of ultrasonic signal are obtained by using Fourier transform technique. Phase-modulation property of optical fiber sensor is discussed and experiment results are also analyzed,which shows that the system could be used to detect the ultrasonic frequency characteristics on the surface of the solid plate transmission.