  A representation of the quantum superalgebra Uq(sl(M+1|N+1)) is constructed
based on the q-differential operators acting on the coherent states
parameterized by coordinates. These coordinates correspond to the local ones of
the flag manifold. This realization provides us with a guide to construct the
free field realization for the quantum affine superalgebra Uq^(sl(M+1|N+1)) at
arbitrary level.
