The issue of vehicles wading water is a highly concerning engineering problem. The smoothed particle hydrodynamics (SPH) method has been widely used to simulate fluid-solid interaction (FSI) problems. Traditional fixed-ghost particle boundary techniques are commonly used to establish boundary conditions for SPH simulations of fluid dynamics. However, these methods encounter difficulties when dealing with complex geometric configurations. Consequently, this study introduces a single-layer particle technique to construct complex geometric shapes. Additionally, an improved boundary technique is proposed to accommodate uneven single-layer particle distribution and effectively prevent particle penetration. After verifying the benchmark case of a cylinder falling into the water, this article adopts the improved single-layer boundary technique to simulate the problem of vehicle wading. The SPH simulation results are in good agreement with the reference results, which demonstrates that the improved single-layer boundary technique proposed in this paper can accurately simulate the vehicle wading problem of complex geometric configurations.