  $B_s^0\rightarrow D_s^{-}$ and $B_s^0\rightarrow D_s^{*-}$ weak transition
form factors are estimated for the whole physical region with a method based on
an instantaneous approximated Mandelstam formulation of transition matrix
elements and the instantaneous Bethe-Salpeter equation. We apply the estimated
form factors to branching ratios, CP asymmetries and polarization fractions of
non-leptonic decays within the factorization approximation. And we study the
non-factorizable effects and annihilation contributions with the perturbative
QCD approach. The branching ratios of semi-leptonic $B_s^0\rightarrow
D_s^{(*)-}l^+\nu_l$ decays are also evaluated. We show that the calculated
decay rates agree well with the available experimental data. The longitudinal
polarization fraction of $B_s\rightarrow D_s^*V(A)$ decays are $\sim0.8$ when
$V(A)$ denotes a light meson, and are $\sim0.5$ when $V(A)$ denotes a $D_q$
($q=d,s$) meson.
