Let Mn be an n(≧ 3)-dimensional compact, simply connected Riemannian manifold without boundary and Sn be the unit sphere of the Euclidean space Rn+1. By two different means we derive an estimate of the diameter whenever the manifold considered satisfies that the sectional
curvature KM ≦ 1, while Ric (M) ≧
(1 + η)V (Sn) for some positive number η depending only on n. Consequently, a gap phenomenon of the manifold will be given according to the estimate of the diameter.