The single-moored light buoys employed in the lower reaches of the Yangtze River play an important role in indicating ship navigation and ensuring safety. To clarify the interaction between waves and floating buoys moored to the riverbed, this paper applies a numerical approach to investigate the wave-induced motion performance of a light buoy and reveal the effects of different mooring configurations to extend its service life. An open-source smoothed particle hydrodynamics (SPH)-based numerical model named dualsphysics coupled with MoorDyn is implemented. This coupled model is validated by simulating the motion of a moored rectangle buoy in regular waves, and compared with experimental data and the numerical results of reef3d code, a mesh-based computational fluid dynamics (CFD) model. The validation results show that the coupled model reproduces experimental data well and has a smaller deviation in comparison with reef3d. Then, the coupling model is applied to simulate the hydrodynamic performance of the real-size light buoy employed in Yangtze River and investigate the effects of encounter angle between wave propagation direction and mooring chain. The results demonstrate the capability of this coupled mooring model to simulate the motion of a moored buoy in regular waves, and this numerical approach will be extended to simulate the light buoy in more complex environments such as irregular waves, flow or extreme weather in further work.