Ancient solution to Kahler-Ricci flow

In this paper, we prove that any non-flat ancient solution to K\"ahler-Ricci flow with bounded nonnegative bisectional curvature has asymptotic volume ratio zero. We also prove that any gradient shrinking solitons with positive bisectional curvature must be compact. Both results generalize the corresponding earlier results of Perelman in \cite{P1} and \cite{P2}. The results can be applied to study the geometry and function theory of complete K\"ahler manifolds with nonnegative bisectional curvature via K\"ahler-Ricci flow. It also implies a compactness theorem on ancient solutions to K\"ahler-Ricci flow.