Abstract: In this parer,for analyzing reliability of control system of the TGP fivestep lock,fault tree analysis(FTA) is introduced,and a fault tree model of the contro l system is established.And the qualitative and quantitative analyses are perform ed for the two redundant systems,and mean time between fault(MTBF) is calculated.On the basis of the analysis,a method is put forward to improve decisionmaking r elability by adding simulation model to parallel connection redundant structure.