  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. 
On K\"ahler manifolds with positive orthogonal bisectional curvature