  We analyze the decay $D_s\to \phi \pi$ with QCD factorization in the heavy
quark limit. The nonfactorizable contributions, including hard spectator
contribution are discussed and numerical results are presented. Our predictions
on the branching ratio of the decay are in agreement with the experiment. We
also use a pure phenomenological method to estimate the branching ratio for
$D_s\to \phi\pi$ with the existed $D^0\to K^{*}\pi$ data.
