Comprehensive reliability analysis of the support structure of a floating offshore wind turbine is implemented by utilizing a hierarchical Bayesian network model that consists of failure propagation and failure behavior layers. In the failure propagation layer, failure probability, reliability, failure rate, mean time to failure with respect to service time are estimated. Moreover, the primary failure contributors to the support structure are determined. In the failure behavior layer, correlations among failure modes are investigated, based on which, impacts of each failure mode on others are clarified. The results of this study are verified by comparing with what was concluded by the fault tree analysis. Recommendations such as the maintenance interval of the support structure should be less than 101 days within the service time of nine years and operational skill training for operators are concluded.