  The equivariant cohomology ring of a GKM manifold is isomorphic to the
cohomology ring of its GKM graph. In this paper we explore the implications of
this fact for equivariant fiber bundles for which the total space and the base
space are both GKM and derive a graph theoretical version of the Leray-Hirsch
theorem. Then we apply this result to the equivariant cohomology theory of flag
varieties.
