Hydraulic system structure is complex and its maintenance is difficult.Therefore,the reliability assessment of the hydraulic system plays an important role in production safety of enterprise.Combined with fault tree analysis and dynamic Bayesian network,an evaluation model was established to analyze the reliability of hydraulic system.The inference function of dynamic Bayesian network was used to obtain the variation law of hydraulic system reliability and availability over time,and to realize hydraulic system fault diagnosis and identify key fault factors.The research results show that the reliability of the hydraulic system will gradually decrease over time,but regular maintenance can keep the availability of the hydraulic system at a high level for a long period of time.The experimental results provide reference for daily maintenance and repair of the hydraulic system.