Abstarct: There are methods for assessing the reliability and safety of complex systems. One of these methods is fault tree analysis as a tool to evaluate and recommend system improvement. A generalization of this method, when the failure behavior is time dependent, is the Pandora temporal fault tree analysis. In the fault tree analysis and Pandora temporal fault tree analysis, accurate system component failure data is usually used to calculate the probability of a tree of top event occurring. However, obtaining this accurate data due to incorrect and inaccurate information about the components of a system can be problematic. This dissertation present the reliability of systems baxsed on fault tree analysis in inaccurate conditions. After reviewing the sets and calculations of fuzzy numbers, as well as reviewing the concepts of reliability and fault tree, the fault tree analysis is presented on the basis of alpha-cut. Analysis of the Pandora temporal fuzzy fault tree using usual fuzzy operators for addition and multiplication as well as the drastic T-norm is another topic discussed in this study. The efficiency of the proposed methods is also shown on real data.