As an important means to improve the reliability of complex manufacturing systems and to ensure that they can function better, condition monitoring systems (CMS) are usually designed and used in manufacture industries. And reliability is one of the most important characteristics of CMS. Fuzzy set theory based on reliability modeling and analysis methods for CMS are proposed in this paper. The methods include a fuzzy graph modeling technique for analyzing the system reliability of CMS, and fuzzy reliability computing methods to quantify uncertainties in function decomposition of CMS and compute system reliability of CMS by invoking Fuzzy-set theory and approaches. On the other hand, the fuzzy reliability of CMS based on fuzzy failure subset and confidence level is defined, and system reliability indexes of CMS are set up to compute the system reliability of CMS. A case of application is used to illustrate the procedure.