The intermediate raft is key to a floating raft vibration isolation system due to the influences of its mass distribution and size on the performance of the system. In light of this situation， the topological optimization method and power flow are introduced to optimize the raft structure by decreasing its weight， and uncover the vibration transfer characteristics of the system respectively. To study the optimized raft structure， the experimental model of floating raft isolation system is built from an air spring isolator， and the isolation performance of floating raft system is analyzed based on the vibration level drops. The simulation shows that the optimized raft structure maintains the desired performance when the weight is greatly reduced. The experiments present a close relation between the vibration isolation results of the air spring and its stiffness， and reinforce the advantages of the improved floating raft vibration isolation system.