  We show that the super D-string action is exactly equivalent to the IIB
Green-Schwarz superstring action with some "theta term" in terms of the path
integral. Since the "theta term" imposes the Gauss law constraint on the
physical state but contributes to neither the mass operator nor the constraints
associated with the kappa symmetry and the reparametrization, this exact
equivalence implies that the impossibility to disentangle the first and second
class fermionic constraints covariantly in the super D-string action is
generally inherited from the IIB Green-Schwarz superstring action except
specific gauge choices which make the ground state massive, such as the static
gauge. Moreover, it is shown that if the electric field is quantized to be
integers, the super D-string action can be transformed to the IIB Green-Schwarz
superstring action with $SL(2, Z)$ covariant tension.
