  Based on a sample of 7.8 million BESI $J/\psi$ events, the decay of $ J/\psi
\to \omega \pi^+ \pi^-$ is studied. A low mass enhancement in the $\pi^+ \pi^-$
invariant mass spectrum recoiling against $\omega$ particle is clearly seen
which does not come from the phase space effect and the background. According
to PWA analysis, this low mass enhancement is a broad $0^{++}$ resonance, the
$\sigma$ particle. If a Breit-Winger function of constant width is used to fit
the $\sigma$ signal, its mass and width are $384 \pm 66$ MeV and $458 \pm 100$
MeV respectively, which correspond to the pole position at (434 $\pm$ 78) - $i$
(202 $\pm$ 43) MeV.
