Abstract: Deepwater BOP system is the core equipment for deepwater well control.It was the failure of such system that led to the oil spill of Macondo well.To understand why such failure occurred,the fault tree analysis was made,and together with the analysis of failure process,a fault tree for system failure with 14 events was built.By solving the minimal cut sets and path sets,10 failure modes are identified to calculate the structural importance for basic events,it was found that the BOP system failure in Macondo accident was mainly attributed to shear plane on pipe joints,inside BOP valve not closed,and leakage of underwater hydraulic accumulator.The probability value of the BOP system failure is consistent with the real case of accident,which demonstrates the validity of the failure analysis.The research is favorable to further investigate the Macondo oil spill,and also provides a theoretical reference for design and application of deepwater BOP.