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The subtransient reactance Xd′′and transient reactance Xd′of large-capacity alternators are crucial parameters to determine the fault current magnitude and design the protection system for the machine. The traditional calculation method of Xd′′and Xd′will bring errors in the graphical decomposition process which depends on the subjective judgement of different individuals, and the analytical method is also inherently imprecise. In this paper, the superconductor simulation method (SSM) incorporated with field-circuit coupled finite element model is presented. The SSM has high accuracy and is capable of considering the saturation effect, skin effect and arbitrary structure of the machine. The unsaturated and saturated values of Xd′′and Xd′of a pumped storage machine are calculated with the proposed SSM. The method of establishing the field-circuit coupled model, governing equations and the superconductor simulation method are introduced in detail. The short-circuit test is conducted on the real machine and the calculated results of both Xd′′and Xd′are verified by the measured values.