  Let $\Sigma$ be a compact convex hypersurface in ${\bf R}^{2n}$ which is
P-cyclic symmetric, i.e., $x\in \Sigma$ implies $Px\in\Sigma$ with P being a
$2n\times2n$ symplectic orthogonal matrix and satisfying $P^k=I_{2n}$,
$ker(P^l-I_{2n})=0$ for $1\leq l< k$, where $n, k\geq2$. In this paper, we
prove that there exist at least $n$ geometrically distinct closed
characteristics on $\Sigma$, which solves a longstanding conjecture about the
multiplicity of closed characteristics for a broad class of compact convex
hypersurfaces with symmetries(cf.,Page 235 of \cite{Eke1}). Based on the proof,
we further prove that if the number of geometrically distinct closed
characteristics on $\Sigma$ is finite, then at least $2[\frac{n}{2}]$ of them
are non-hyperbolic; and if the number of geometrically distinct closed
characteristics on $\Sigma$ is exactly $n$ and $k\geq3$, then all of them are
P-cyclic symmetric, where a closed characteristic $(\tau, y)$ on $\Sigma$ is
called P-cyclic symmetric if $y({\bf R})=Py({\bf R})$.
