The optimal non-contact onboard power source for superconducting electrodynamics suspension (EDS) maglev is the linear generator. As a result, the development of the linear generator has been significantly aided by the research of its properties. A method for figuring out the maximum output power of the EDS maglev's linear generator is suggested. It has the advantages of a straightforward formulation, quick calculation time, and acceptable precision. First, the electromagnetic model of the linear generator taking into account the eddy current loss of the outer vessel is constructed in accordance with the structure of EDS maglev. Second, the magnetic flux density of superconducting (SC) coils and the multi-structure figure-8 shaped coils containing harmonic components are expressed using Fourier coefficients utilizing the harmonic magnetic field approach, and this is done by incorporating the structural correction coefficient of SC coils. Third, it is proposed to use variable resistance to equivalent eddy current losses to calculate the linear generator's maximum output power. Finally, the finite element (FEM) simulation and the measurement data of the Yamanashi line are used to confirm that the theory is valid.