  In this paper, we construct the additional symmetries of the supersymmetric
BKP(SBKP) hierarchy. These additional flows constitute a B type $SW_{1+\infty}$
Lie algebra because of the B type reduction of the supersymmetric BKP
hierarchy. Further we generalize the SBKP hierarchy to a supersymmetric
two-component BKP (S2BKP) hierarchy equipped with a B type
$SW_{1+\infty}\bigoplus SW_{1+\infty}$ Lie algebra. As a Bosonic reduction of
the S2BKP hierarchy, we define a new constrained system called the
supersymmetric Drinfeld-Sokolov hierarchy of type D which admits a $N=2$
supersymmetric Block type symmetry.
