Abstract: Scale effect evaluation is the foundation for designing scaled flight test conditions and the key to validate the flight data in the development of civil aircraft. Based on geometric similarity and dynamic similarity criteria, the present paper utilizes computational fluid dynamics to analyze the effects of similarity criteria parameters such as Mach number, Reynolds number, and Froude number on aerodynamic loads, aerodynamic coefficients, and elastic deformation for a civil aircraft and its scaled model. Results demonstrate that when the dynamic similarity is satisfied, the differences between the prototype and its scaled model come from the Mach number whereas the effects of the Reynolds number is relatively small. When the prototype is flying at low Mach numbers (Ma < 0.5) , the compression effects are not significant, and the scaled prototype exhibits similar spanwise and chordwise load distribution characteristics, with typical stability coefficients and control coefficients differing by approximately 10%, which is within the robustness range for control law design. Furthermore, when maintaining similar mass and stiffness distributions, the maximum deflection of the wingtip twist does not exceed 0.5°, and the maximum deflection does not exceed 0.5%, which are acceptable for engineering applications.