  The $B_{u,d,s}\to V,A$ form factors are studied in perturbative QCD approach
($V,A$ denote a vector meson and two kinds of p-wave axial-vector mesons:
$^3P_1$ and $^1P_1$ states, respectively.). The form factors are directly
studied in the large recoiling region and extrapolated to the whole kinematic
region within the dipole parametrization. Adopting decay constants with
different signs for the two kinds of axial-vectors, we find that the two kinds
of $B\to A$ form factors have the same sign. The two strange mesons $K_{1A}$
and $K_{1B}$ mix with each other via the SU(3) symmetry breaking effect. In
order to reduce the ambiguities in the mixing angle between $K_{1A}$ and
$K_{1B}$, we propose a model-independent way that utilizes the B decay data.
Most of the branching fractions of the semilteptonic $B\to Al\bar \nu_l$ decays
are of the order $10^{-4}$, which still need experimental tests in the on-going
and forthcoming experiments.
