Study On The Structures Of Projective Manifolds Polarized By An Ample Line Bundle

In this paper, it tries to explore the structure of manifolds through the nef value of the ample line bundle on the projective manifold.It mainly uses the Mori theory to study the structure of a n-dimensional projective manifold.The results as:Let X be a n-dimensional projective manifold and L be an ample line bundle over X.Ï„=u is the nef value of L.If the second Betti number of X is one,then X is a Fano manifold of index one;If u=n+1,then X is Pn;If u=n, X is either Qn or a Pn-1 -bundle over a smooth curve.