Abstract:  As key component of well control system, the reliability of deepwater blowout preventer (BOP) is extremely important to guarantee the safety and high efficiency of deepwater drilling. By analyzing failure accident cases in Gulf of Mexico and the South China Sea, combining security bulletins and maintenance experience of field failures, we analyze the failure mode of HYSY981 BOP system, perform failure mode and effect analysis (FMEA) of wellhead and sorted risk factors scientifically based on information evaluation model combined with risk priority number (RPN). Analysis results show that with the proposed method, we can find out the potential risk factors affecting the reliability of BOP system, and provide basis for operators to achieve the goal of deepwater BOP system reliability from risk prevention and control measures, risk treatment scheme, optimization of parts inventory, etc.