  As one candidate of the higher dimensional black holes, the 5D Ricci-flat
black string is considered in this paper. By means of a non-trivial potential
$V_{n}$, the quasi-normal modes of a massless scalar field around this black
string space is studied. By using the classical third order WKB approximation,
we analyse carefully the evolution of frequencies in two aspects, one is the
induced cosmological constant $\Lambda$ and the other is the quantum number
$n$. The massless scalar field decays more slowly because of the existences of
the fifth dimension and the induced cosmological constant. If extra dimension
has in fact existed near black hole, those quasi-normal frequencies may have
some indication on it.
