In Takagi and Sugeno (T–S) fuzzy fault tree analysis (FFTA), the construction of T-S fuzzy gates relies too much on expert experience, which will result in inevitable subjective errors. In order to overcome this disadvantage, a new method was proposed which combined importance index with T-S fuzzy fault tree model to evaluate reliability of the events. The importance index of components can be solved through Monte Carlo (MC) simulation. The proposed method is suitable for systems where exact information on the fault probabilities of the components and the magnitude of failure and effect on system are not available. The concept and calculation method of T-S probability importance was presented. Finally, the feasibility of the method is verified by analyzing the reliability of the sealing subsystem of the NC turret and the weak links of the system are obtained by the importance analysis, which will provide data for system fault diagnosis and preventive maintenance.