The investigation of mechanical response characteristics of nanocrystalline metallic materials under extreme high-pressure conditions possesses significant scientific importance and engineering value. Using a diamond anvil cell combined with synchrotron radiation X-ray diffraction techniques, the mechanical behavior of palladium (Pd) with an average grain size of approximately 10 nm under static high pressure was studied. Within the investigated pressure range (0−111 GPa), the crystal structure of palladium remained stable. Analysis of diffraction peak positions and full width at half maximum (FWHM) at each pressure point enables determination of unit cell volume, grain size, and microscopic strain under high-pressure conditions. Fitting with the third-order Birch-Murnaghan equation yields bulk modulus of 288 GPa (hydrostatic) and 290 GPa (non-hydrostatic), and the yield strength is approximately 20 GPa. In addition, by integrating existing literatures, this study systematically explored the influence of size effects on mechanical properties. The yield strength of Pd progressively increases with decreasing grain size, exhibiting a 300% enhancement compared to Pd nanofibers. These findings provide crucial data for the structural design and application of nanocrystalline Pd under extreme conditions.