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Abstract: The finite-difference method (FDM) is an essential tool in exploration geophysics, particularly for simulating wave propagation in fluid-solid coupled media. Despite its widespread use, FDM faces significant challenges that affect its accuracy and efficiency. Firstly, the implicit handling of fluid-solid boundary conditions through parameter averaging strategy often results in low simulation accuracy. Secondly, surface topography can introduce staircase diffraction noise when grid spacing is large. To address these issues, this paper presents a novel approach. We derive an implicit expression for fluid-solid boundary conditions based on average medium theory, translating explicit boundary conditions into model parameter modification. This enables implicit handling of fluid-solid boundaries by modifying the parameters near the boundary. Furthermore, to mitigate staircase diffraction noise, we employ multiple interface discretization based on the superposition method. This effectively suppresses staircase diffraction noise without requiring grid refinement. The efficacy of our method in accurately modeling wave propagation phenomena in fluid-solid coupled media is demonstrated by numerical examples. Results align well with those obtained using the spectral element method (SEM), with significant reduction in staircase diffraction noise.