  The light-front distribution amplitudes (LFDAs) and the decay constant of the
$K $ pseudoscalar meson are extracted within the framework of the AdS/QCD
correspondence. For the LFDAs calculation, we consider a momentum-dependent
(dynamical) helicity wave function which contains the dynamical spin effects.
We use the LFDAs to predict the transition form factors of the semileptonic
$B\to K \ell^{+}\ell^{-}$ decay. With the help of these form factors, the
differential branching ratio of the $B\to K\, \mu^+ \mu^-$ on $q^2$ is plotted.
A comparison is made between our prediction in AdS/QCD and the results obtained
from two models including the light-cons sum rules (LCSR) and lattice QCD as
well as the experimental values.
