Abstract: To enhance the precision of thermal neutron absorption cross-section measurements for natural gadolinium, this study presents a numerical inversion method based on the prompt gamma-ray spectrum generated from thermal neutron activation. The proposed approach establishes an energy-to-counts conversion model between characteristic X-rays and prompt gamma-rays within a defined energy window, enabling the quantitative determination of cross-section parameters. This method effectively mitigates errors typically introduced by tissue inhomogeneity and complex geometric modeling in conventional measurement techniques. A gadolinium disk (ϕ 50 mm × 1 mm) is used in Monte Carlo simulations under 0.025 eV thermal neutron irradiation. Spectral features in the 40-200 keV range are extracted to derive energy conversion coefficients and perform cross-section inversion. The results indicate that the measured thermal neutron absorption cross-section of natural gadolinium is 47 448 barns, showing excellent agreement with reference database values and demonstrating high accuracy and robustness of the proposed method.