Today, suppliers have a very important role for companies and organizations and proper choice of suppliers can be considered as an important competitive advantage in the market for companies and organizations. Since suppliers have a close relationship with organizations, their final production and services depend on suppliers both in terms of quality and cost. One of the solutions in critical situations and disruptions is the use of reliable suppliers to overcome critical situations and provide raw materials. In this paper, the reliability of the supplier is estimated by examining supplier disturbances and considering the relationship between them and using the Failure Tree Analysis (FTA) technique . Fuzzy theory approach is used due to the precision of input information. In this paper, the validation model provided of the two suppliers of the sub-surface research institute in Isfahan has been evaluated for validation of the model.