With the growing demand for cost-effective and reusable launch systems, traditional expendable rockets are becoming increasingly unsuitable for frequent and large-scale aerospace missions. Reusable launch vehicles (RLVs) have become a major focus in modern space transportation, in which the development of safe and efficient recovery mechanisms is essential for achieving low-cost operations and long-term sustainability. Among these mechanisms, the landing buffer system plays a key role in absorbing impact energy and maintaining structural strength during descent and landing. This study aims to design a rocket recovery buffer system based on multibody dynamics, with a particular focus on how the structure and spatial co-location of hydraulic cylinders affect recovery performance. To this end, a parametric rigid-flexible coupled dynamic model of the recovery system is developed to systematically investigate hydraulic actuators configurations, accurately describing the interaction between structural flexibility and multibody motion throughout the landing process. By simulating a series of rocket recovery cases with different descent speeds, suitable hydraulic cylinder parameters are selected to ensure that the system meets energy absorption and load-bearing requirements. Then, the optimal spatial placement of the cylinders is determined, thereby enhancing the overall buffering performance under given structural constraints. Furthermore, to evaluate the robustness and reliability of the optimized design, a shooting method based on low-discrepancy sequences is applied to assess the probability of successful rocket recovery under varying conditions. The research provides both theoretical support and a practical engineering method for the high-performance design of buffer systems in reusable launch vehicles, contributing to the advancement of reliable and cost-effective space launch technologies.