Sodium displays a great deal of surprising behaviors under high pressure such as melting at room temperature at 118GPa and transition to an insulator over 200GPa. Recent HPCAT experiments measured plasmon excitations of sodium from ambient pressure up to 97GPa using the momentum-dependent inelastic X-ray scattering technique. The square of zero-momentum plasmon energy increases linearly with densification up to 1.5-fold (~5GPa), which agrees well with a simple free-electron model prediction. From 1.5-fold to 3.7-fold densification at 97GPa, the linear relation curves towards the density axis. However, this deviation can still be explained by a simple metal model. These results showed that even under multiple fold densification the solid Na of both bcc and fcc symmetry can be regarded as simple metals.