Highly precise structural analysis of tension-stabilized space reflectors using geometrically nonlinear finite-element (FE) model usually requires accurate knowledge of the design parameters. However, internal forces in the deformed configuration or temporal change of stiffness parameters are usually unable to be measured; thus, accurate numerical modeling of a tension-stabilized structure is difficult. The present paper describes a methodology to construct a high-fidelity FE model of high-precision gossamer structures by applying a conventional method of FE model updating to a geometrically nonlinear FE analysis. Using the FE model updating methodology, an accurate FE model can be constructed through the estimation of unmeasured parameters. In this study, a simple tension-stabilized beam structure is analyzed for demonstration of the concept.