Abstract: Strain-gauge balances are widely employed in wind tunnel tests for aerodynamic force measurements. The temperature effect, originating from the thermal structural deformation induced by temperature gradient loading, constitutes a significant yet often overlooked source of measurement uncertainty. Using the finite element method, this study establishes a simulated calibration formula for the balance and analyzes its strain response under combined temperature gradient load and mechanical loads. The thermomechanical coupling mechanism is systematically investigated. Results indicate that under pure temperature gradient loading, the resulting thermal deformation exerts a negligible influence on all components of the balance. In contrast, under simultaneous temperature gradient and mechanical loading, the X component exhibits the largest deviation, reaching 0.16% of its design range, while other components remain largely unaffected. Ground test results align well with the simulation trends. The essence of the thermo-mechanical coupling temperature effect lies in the interaction between thermal structural deformation caused by temperature gradient loading and mechanical deformation caused by mechanical loadings, which has a certain impact on the measurement uncertainty of the axial force of the balance. This study not only identifies the sources of measurement uncertainty in the axial force of the balance, but also lays a theoretical foundation for establishing a correction strategy for the thermo-mechanical coupling temperature effect of the strain balance.