<p>Thin-walled steel tubes are widely recognized for their energy absorption performance and are commonly used in protective structures across fields such as blast impact, vehicle transportation, and marine engineering. However, their application in mitigating rockfall hazards remains underexplored, particularly under high-energy impact conditions. This study developed a numerical model in LS-DYNA to investigate the deformation and energy absorption of the thin-walled steel tube under the impact of rockfall. Key parameters, such as energy absorption efficiency, ultimate energy absorption, crushing force efficiency, and impact force transmission rate, were examined to evaluate the influence of wall thickness, diameter, and bottom support materials on the tube’s energy absorption performance. The results show that steel tube deformation proceeds through four stages: elastic deformation, buckling, recovery, and stabilization. Increasing wall thickness enhances energy absorption efficiency but also leads to higher crushing force and impact force transmission rate. Larger diameters reduce crushing force and improve ultimate energy absorption, though this comes at the cost of lower energy absorption efficiency. While bottom support materials have minimal impact on the tube’s energy absorption efficiency, increasing the deformation modulus in these materials results in greater impact force transmission rate. Furthermore, a multi-objective optimization considering the combined effects of energy absorption and impact force identifies the optimal structural parameters, which not only guides the selection of steel tubes, but also provides practical value for the engineering design of rockfall protection systems in real-world applications.</p>