  We study $e^+e^-\to\pi^+\pi^-$ cross section and phase shift of $I=l=1$
$\pi-\pi$ scattering below 1GeV in framework of chiral constituent quark model.
The results including all order contribution of the chiral perturbation
expansion and all one-loop effects of pseudoscalar mesons, but without any
adjust parameters. Width of $\rho$ predicted by the model strongly depends on
transition momentum-square $q^2$. We show that the mass pamameter of
$\rho$-meson in its propagator is very different from its physical mass due to
momentum-dependent width of $\rho$. The mass difference between $\rho^0$ and
$\omega$ are predicted successfully. The rigorous theoretical prediction on
$e^+e^-\to\pi^+\pi^-$ cross section and the phase shift in $I=l=1$ $\pi-\pi$
scattering agree with data excellentlly.
