  The branching ratios and CP asymmetries of
  $B\to \pi\pi$ decays measured in B factory experiments indicate a large ratio
of color-suppressed ($C$) to color-allowed ($T$) tree contributions and a large
relative phase between the tree and penguin amplitude. In this talk, I would
like to report on a recent analysis to see whether the large $C/T$ ratio can be
explained within the QCD based model with i) a large contribution from the
annihilation terms or with ii) large final-state-interaction phase between two
different isospin amplitudes. We show that the current experimental data do not
exclude either possibility but we may be able to distinguish these two effects
in future measurements of direct CP asymmetry in $B\to \pi^{0}\pi^{0}$ decay.
