A 5x5 partial fuel assembly was used for a comparative design evaluation test of a newly developed spacer grid from a mechanical/hydraulic vibration aspect. Axial flow pattern along this rod bundle in the test was very complex due to the intermediate spacers and the mixing vane; Understanding of this flow field of a dynamic pressure is a preliminary step for a theoretical analysis of a vibratory behavior of a partial fuel assembly. Since a fluctuating pressure induced by the randomly-varying flow turbulence cannot be accurately predicted by an analysis alone, it has to be measured directly on the surface over the rod or in an accessible vicinity of the bundle. In this study, the fluctuating pressure acting on a partial fuel assembly with a spacer grid and a mixing vane was measured. The measured PSD showed different spectral features from the results of the literatures and had a series of periodic pulsations with sidebands over the specific frequency ranges; it is believed that the periodic components in the PSD have to do with the design of the spacer grid and the mixing vane. And, the exciting force function for the theoretical analysis of a partial fuel assembly with spacers and a mixing vane was estimated as a possible PSD form.