Aiming at the problem of insufficient structural reliability analysis of meta-action units, a reliability evaluation method of meta-action units based on the fault tree Bayesian network is proposed. Firstly, the composition diagram of the ball screw element action unit is modeled and analyzed. The element action unit's abnormal operation fault tree is established using fault mode and impact analysis. The Bayesian network structure of the meta-action unit fault tree is adopted to enhance the failure traceability reasoning function and realize the optimization of the reliability evaluation function of the metaaction unit of the ball screw. Finally, the rationality of the model is proved by taking the unit test bench of the ball screw element as an example.