A railway substation transforms the electric power transmitted from electric power plants and supplies it to the railway power system for the appropriate operation of traction system. For the appropriate operation of the traction system, it is very important to maintain the security of electric power system. This paper proposes the case when an AC railway substation does not operate right, and Fault Tree(FT), Event Tree(ET) and Minimal Cut Sets(MCS) algorithm to calculate the reliability indices of railway substation. Event tree is created and gate results of fault tree analysis are used as the source of event tree probabilities. Fault tree represents the interaction of failures and basic events within a system. Minimal Cut Sets analysis is used to minimize system errors, Event Tree and Fault Tree analysis result is helpful to assessing the reliability to interpreted. The reliability indices can be used to determine the equipment to be replaced for the entire system reliability improvement.