  In this paper, we study any K\"ahler manifold where the positive orthogonal
bisectional curvature is preserved on the K\"ahler Ricci flow. Naturally, we
always assume that the first Chern class $C_1$ is positive. In particular, we
prove that any irreducible K\"ahler manifold with such property must be
biholomorphic to $\mathbb{C}\mathbb{P}^n. $ This can be viewed as a
generalization of Siu-Yau\cite{Siuy80}, Morri's solution \cite{Mori79} of the
Frankel conjecture. According to [8], note that any K\"ahler manifold with
2-positive traceless bisectional curvature operator is preserved under Kahler
Ricci flow; which in turns implies the positivity of orthogonal bisectional
curvature under the flow.
