  In this work, we study the localized $CP$ violation and the branching
fraction of the four-body decay $\bar{B}^0\rightarrow K^-\pi^+\pi^-\pi^+$ by
employing a quasi-two-body QCD factorization approach. Considering the
interference of $\bar{B}^0\rightarrow \bar{K}_0^*(700)\rho^0(770)\rightarrow
K^-\pi^+\pi^-\pi^+$ and $\bar{B}^0\rightarrow \bar{K}^*(892)f_0(500)\rightarrow
K^-\pi^+\pi^-\pi^+$ channels, we predict $\mathcal{A_{CP}}(\bar{B}^0\rightarrow
K^-\pi^+\pi^-\pi^+)\in[0.15,0.28]$ and $\mathcal{B}(\bar{B}^0\rightarrow
K^-\pi^+\pi^-\pi^+)\in[1.73,5.10]\times10^{-7}$, respectively, which shows that
this two channels' interference mechanism can induce the localized $CP$
violation to this four-body decay. Meanwhile, within the two quark model
framework for the scalar mesons $f_0(500)$ and $\bar{K}_0^*(700)$, we calculate
the direct CP violations and branching fractions of the $\bar{B}^0\rightarrow
\bar{K}_0^*(700)\rho^0(770)$ and $\bar{B}^0\rightarrow \bar{K}^*(892)f_0(500)$
decays, respectively. The corresponding results are
$\mathcal{A_{CP}}(\bar{B}^0\rightarrow \bar{K}_0^*(700)\rho^0(770)) \in [0.20,
0.36]$, $\mathcal{A_{CP}}(\bar{B}^0\rightarrow \bar{K}^*(892)f_0(500))\in
[0.08, 0.12]$, $\mathcal{B} (\bar{B}^0\rightarrow
\bar{K}_0^*(700)\rho^0(770)\in [6.76, 18.93]\times10^{-8}$ and $\mathcal{B}
(\bar{B}^0\rightarrow \bar{K}^*(892)f_0(500))\in [2.66, 4.80]\times10^{-6}$,
respectively, indicating the $CP$ violations of these two two-body decays are
both positive and the branching fractions are quite different. These studies
provide a new way to investigate the aforementioned four-body decay and could
be helpful in clarifying the configuration of the structure of light scalar
meson.
