The authors developed the structural design process on the basis of experimental SEA for reducing structure-borne sound. However, it was difficult to predict the sound pressure accurately in order not to predict the variation of vibration input power by structural modification. There are four steps in the process, at the third steps, the process identifies the internal loss factors (ILFs) or the coupling loss factors (CLFs) which should be changed in order to reduce the noise radiated from the machinery using sensitivity analysis to the squared sound pressure at the evaluation point. The sensitivity analysis is based on the perturbation method, the squared sound pressure or the vibration energy are evaluated regarding the variation of respective loss factors and input power. For two SEA models are used with and without predicted vibration input power by structural modification, parameter study are implemented by analytical SEA. As a result, it can be seen that sound energy values for the SEA model without using the predicted vibration input power for structural modification by a partial thickness change are overestimated for a flat plate. The same phenomenon for L shaped plate was also confirmed by the experimental test.