  In Perturbative QCD (PQCD) approach we study the direct $CP$ violation in the
pure annihilation decay process of
$\bar{B}^0_{s}\rightarrow\pi^+\pi^-\pi^+\pi^-$ induced by the $\rho$ and
$\omega$ double resonance effect. Generally, the $CP$ violation is small in the
pure annihilation type decay process. However, we find that the $CP$ violation
can be enhanced by double $\rho-\omega$ interference when the invariant masses
of the $\pi^+\pi^-$ pairs are in the vicinity of the $\omega$ resonance. For
the decay process of $\bar{B}^0_{s}\rightarrow\pi^+\pi^-\pi^+\pi^-$, the
maximum $CP$ violation can reach 28.64{\%}.
