  It is very important to know the strength of annihilation contribution in B
charmless nonleptonic decays. $\bar{B}_{s}\to \pi^{+}\pi^{-}$ process could
serve a good probe of the strength. We have studied the process in QCD
factorization framework. Using a gluon mass scale indicted by the studies of
infrared behavior of gluon propagators to avoid enhancements in the soft end
point regions, we find that the CP averaged branching ratio is about
$1.24\times 10^{-7}$, the direct CP asymmetry $C_{\pi\pi}$ is about -0.05,
while the mixing-induced CP asymmetry quite large with the value
$S_{\pi\pi}$=0.18. The process could be measured at LHC-b experiments in the
near future and would deepen our understanding of dynamics of B charmless
decays.
