  We obtain the superfluid hydrodynamic equations of a multi-component Bose gas
with short-ranged interactions at zero temperature under the local equilibrium
assumption and show that the quantum pressure is generally present in the
nonuniform case. Our approach can be extended to systems with long-range
interactions such as dipole-dipole interactions by treating the Hartree energy
properly. For a highly symmetric superfluid, we obtain the excitation spectrum
and show that except for the density phonon, all other excitations are all
degenerate.The implication of our results is discussed.
