  We show that the Green's functions in non-linear gauge in the theory of
perturbative quantum gravity is expressed as a series in terms of those in
linear gauges. This formulation is also holds for operator Green's functions.
We further derive the explicit relation between the Green's functions in the
theory of perturbative quantum gravity in a pair of arbitary gauges. This
process involves some sort of modified FFBRST transformations which is
derivable from infinitesimal field-dependent BRST transformations.
