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Superconducting radio-frequency cavities have been chosen as the main accelerating cavities and harmonic cavities in some synchrotron light sources. The previously developed computational scheme for the multiphysics with finite-element models can be used to calculate the electromagnetic characteristics of an externally loaded cavity, but unphysical results could be found on greatly deformed cavities. To solve this problem, we mesh not only the cavity structure with shell elements, but also the cavity vacuum with solid elements at the stage of computing the structural deformation. The interior solid elements, as being assigned with a negligible rigidity, are thus adjusted to a reasonable element shape as the external loads are applied on the shell elements to simulate the real cavity structure; this deformation information is then transferred to compatible electromagnetic elements to compute the electromagnetic characteristics of the deformed cavity. Examples of this improvement are presented with a 1.5-GHz superconducting radio-frequency cavity. Two loading conditions, external pressure and longitudinal compression, are demonstrated in computing the resonance frequency.