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Various principles and algorithms of the wide-area protection system (WAPS) have been developed so far. However, there are few discussions about the foundation in implementation of the WAPS (i.e., the corresponding communication system and its reliability). This paper presents a reliability evaluation method for the communication systems in wide-area protection (CSWAP). First, system structure and characteristics of the CSWAP are hierarchically analyzed from layers of substation communication, regional communication, and wide-area communication. The reliability model based on fault-tree analysis for each layer is then established. Second, three reliability indices are introduced. Third, an index calculation method based on sequential Monte Carlo simulation is proposed, which adopts the idea of static handling, takes into account faults and repairs of components, and overcomes several disadvantages of analytical methods, such as complicated calculation and weak adaptability. Finally, a case of the CSWAP in the IEEE 11-bus system is analyzed to summarize the effect factors of its reliability and demonstrate the validity of the proposed method. The results show that the models have definite physical significance, and the proposed method is helpful for quantitative reliability assessment, influencing factor analysis, and weakness identification.