The characteristic equations of the guided waves in free steel plate and water loaded steel plate are solved based on the Navier kinetic equation; then, the dispersion curves are drawn. After comparing and analyzing the dispersion characteristics of free plate and water loaded plate, it is found that a QuasiScholte modal guided wave exists in water loaded steel plate, which does not exist in free steel plate. Through numerical calculation, finite element simulation and experiment, the propagation characteristics and modals of the guided waves in free plate and water loaded plate are verified respectively. In lowfrequency region, A0 modal exists in the guided waves in free plate, and QuasiScholte modal only exists in the guided waves in water loaded plate. Using the propagation characteristics of the A0 modal and QuasiScholte modal guided waves, a water level measurement experiment was designed, which adopts pitchcatch PZT sensor deployment modal, and a 130Hz, 2.5period Hanning window modulated sine wave signal is used as the test signal. The results show that the water level and the guided wave propagation time exhibit a linear relationship, which can be potentially used for the estimation of water level in a container.