Abstract: Aiming at the issue of load distribution being influenced by the stiffness of vibration isolators in an APU （Auxiliary Power Unit） mounting system, and to clarify the underlying influence mechanisms and the safety of the design margin, a finite element model of the APU mounting system was established. Using a parametric approach, the effects and variation patterns of interface loads were investigated separately as the stiffness of the rear mounting, the forward vertical link, and the right adapter’s vibration isolators varied within a certain range. The results indicate that altering the stiffness of the rear mounting has a negligible impact on the load distribution across all interfaces. When modifying the stiffness of the forward vertical link and the right adapter, the interface loads under forward conditions decreased by up to 12.5%, while the lateral load on the right adapter increased by a maximum of 3.54% as stiffness increased. Under lateral conditions, the load on the forward vertical link increases by up to 8%. The research demonstrates that variations in isolator stiffness do not alter the critical load cases, and all load fluctuations remain within the design margins, thereby ensuring the safety of the mounting system. This study elucidates the mechanism through which stiffness variations influence load distribution, providing a theoretical foundation and design guidance for the engineering application of vibration isolators.