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The cluster manifold becomes an essential part in a subsea production system and it has been widely used in the development of ultra-deepwater oil and gas fields. One hand, it can gather the production fluid from subsea wells. On the other hand, it can distribute water, gas and chemical agents from the floating production system to each subsea well. Hence, the failure of subsea cluster manifolds may not only lead to the stagnation of production wells and economic losses but also cause environmental pollution and human health in severe cases. Therefore, the reliability of subsea cluster manifolds is quite of importance and it should be studied for the safety service of the subsea production system. Based on the fault tree analysis (FTA), this paper will discuss the failure cause of six well slots subsea cluster manifolds in LiWan 3-1 gas field in China South Sea. Considering the pipeline structure, control system and flow assurance, the fault trees of subsea cluster manifolds are built. Meanwhile, the importance degrees of each elementary event are ranked orderly and the minimum cut sets are obtained through analyzing the structure important of the FTA. The failure major reasons are obtained and the preventive measures are proposed, which could have some guiding significance for the operations of subsea cluster manifolds system in China South Sea.