A method is proposed for deriving the equivalent circuit of a superconducting synchronous generator of coreless structure. In deriving the equivalent circuit, account was taken of the nonlinearity of the electromagnetic shield. Linear constants of this equivalent circuit can be calculated directly using design data, and nonlinear constants are determined using the linear constants thus determined. A method is also proposed to linearize the nonlinear equivalent circuit. The equivalent operational impedances obtained by this method make it possible to analyze the behavior of a superconducting generator in the same way as conventional synchronous generators are analyzed.