  The Yukawa corrections of order ${\cal O}(\alpha_{ew}m_{t(b)}^2/m_W^2)$,
${\cal O}(\alpha_{ew}m_{t(b)}^3/m_W^3)$ and ${\cal
O}(\alpha_{ew}m_{t(b)}^4/m_W^4)$ to the width of sbottom decay into lighter
stop plus charged Higgs boson are calculated in the Minimal Supersymmetric
Standard Model. These corrections depend on the masses of charged Higgs boson
and lighter stop, and the parameters $\tan\beta$ and $\mu$. For favorable
parameter values, the corrections decrease or increase the decay widths
significantly. Especially for high values of $\tan\beta$(=30) the corrections
exceed at least 10% for both $\tilde b_1$ and $\tilde b_2$ decay. But for low
values of $\tan\beta$(=4,10) the corrections are small and the magnitudes are
less than 10%. The numerical calculations also show that using the running
bottom quark mass which includes the QCD effects and resums all high order
$\tan\beta$-enhanced effects can improve much the convergence of the
perturbation expansion.
