  The study of exclusive B decays in perturbative QCD are complicated by the
endpoint problem. In order to perform the perturbative calculation, the Sudakov
effects are introduced to regulate the endpoint singularity. We provide a
systematic analysis with leading and next-to-leading twist corrections for
$B\to\pi$ form factors in pQCD approach. The intrinsic transverse momentum
dependence of hadronic wave function and threshold resummation effects are
included in pQCD approach. There are two leading twist B meson distribution
amplitudes (or generally wave functions) in general. The QCD equations of
motion provide important constraints on B meson wave functions. The reliability
of pQCD approach in \bpi form factors is discussed. 70% of the result comes
from the region $\alpha_s(t)/\pi<0.2$ and 38% comes from the region where the
momentum transfer $t\geq 1\GeV$. The conceptual problems of pQCD approach are
discussed in brief. Our conclusion is that pQCD approach in the present form
cannot provide a precise prediction for \bpi transition form factors.
