Based on the attenuation characteristic of leaky-Rayleigh waves at the fluid-solid interface, we propose a method for liquid level detection using the amplitude of leaky-Rayleigh waves. A finite-difference modeling is performed to investigate the impact of different liquid level on the amplitude of leaky-Rayleigh wave generated by a near-surface impulsive plane source in the solid with vibration direction perpendicular to the fluid-solid interface, through which the influence of scattering brought by the gas-liquid interface itself and the energy leak in the propagation process is discussed. The numerical simulation result shows that the influence of the scattering effect of a gas-liquid interface itself very slightly contributes to the amplitude of the leaky-Rayleigh wave and the predominant cause of the attenuation is the energy leak; with the liquid level increases, the amplitude of leaky-Rayleigh wave pulse declines exponentially and its central frequency becomes lower. From this the correlation between the amplitude of leaky-Rayleigh wave and the liquid level is built. We further conduct an experiment, whose result is consistent with our modeling result despite some slight difference in the variation range of the amplitude and the frequency shift. Thus, the feasibility of our method is proved.