Aiming at the dynamic failure characteristics of the hydraulic heightening system, the dynamic fault tree analysis method based on discretetime Bayesian network(DTBN) was used to analysis it. A dynamic fault tree method based on DTBN was studied. The transformation method of dynamic fault tree to DTBN and the method of using DTBN to calculate the failure probability of top event, the posterior probabilities and the Birnbaum importance measures of basic events in each time interval and the mission time using DTBN were given. The dynamic fault tree analysis method based on DTBN was used to construct the dynamic fault tree of the hydraulic heightening system and transform it into DTBN.The Bayesian network bidirectional reasoning system was used to calculate the failure probability of the hydraulic heightening system, the posterior probabilities and the Birnbaum importance measures of each component in each time interval and the mission time, which provides basis for identifying vulnerable components of the system and for improving system reliability.