The wave resistance of a buoy is affected by the mode of anchorage and the buoy structure. Combining the structures and the mode of anchorage of the existing buoys, designing a buoy with significantly improved wave resistance is a major challenge for marine environment monitoring. This work carried out experimental and numerical simulation studies on the hydrodynamic properties of a self-designed symmetrical three-cylinder buoy. The wave resistance of the buoy was analyzed using different wave conditions, and a full-scale simulation of the buoy was performed using the finite element method and lumped mass method. Experimentally, it was found that the symmetrical three-cylinder buoy stability was less affected by the wave height, but mainly by the wave period. Additionally, the effects of wave height and wave period on mooring tension were also studied, and the results showed that mooring tension was mainly affected by wave period, which was explained by the rate of change of the buoy momentum. Finally, a numerical model was proposed for the interpretation of these experiments. Results from numerical simulations for the trajectory of the buoy and the tension of the mooring cable correlated well with the experimental data.