  In this short note we announce a regularity theorem for K\"ahler-Ricci flow
on a compact Fano manifold (K\"ahler manifold with positive first Chern class)
and its application to the limiting behavior of K\"ahler-Ricci flow on Fano
3-manifolds. Moreover, we also present a partial $C^0$ estimate to the
K\"ahler-Ricci flow under the regularity assumption, which extends previous
works on K\"ahler-Einstein metrics and shrinking K\"ahler-Ricci solitons (cf.
\cite{Ti90}, \cite{DoSu12}, \cite{Ti12}, \cite{PSS12}). The detailed proof will
appear in \cite{TiZh13}.
