Abstract: The Dynamic Bayesian Network (DBN) theory is used to assess the reliability of antenna pitching system, and the bottleneck is also recognized. Firstly, Structured Analysis and Design Technique (SADT) is used to analyze the system, and the functional modules are obtained; then by implementing Failure Mode and Effect Analysis (FMEA) on the functional modules, the possible failure modes, failure causes as well as the effects of each functional component are identified. Based on the efforts above mentioned, DBN model of the system is established. Forward reasoning is used for assessing the process of system reliability evolution, and the weakness parts are recognized by backward reasoning. Case study shows that the analysis results are consistent with practical data, it provides theoretical basis for reliability growth of such systems.