We study theoretically the π-electron-hole plasma excitations in single-walled metallic carbon nanotubes within the framework of the classical electrodynamics. The π-electrons and holes of the nanotubes are described by means of the two-fluid hydrodynamic theory. Numerical results show that the low-energy excitations are in qualitative agreement with low-frequency excitations (π plasmon) in experimental observations in the case where the π-electron and hole effective masses are nearly equal.
