  In this paper, a unified dark fluid with constant adiabatic sound speed is
decomposed into cold dark matter interacting with vacuum energy. Based on
Markov chain Monte Carlo method, we constrain this model by jointing the
geometry and dynamical measurement. The geometry test includes cosmic microwave
background radiation from \textit{Planck}, baryon acoustic oscillation, and
type Ia supernovae; the dynamic measurement is $f\sigma_8(z)$ data points which
is obtained from the growth rate via redshift-space distortion, and
$\sigma_8(z)$ is the root-mean-square amplitude of the density contrast
$\delta$ at the comoving $8h^{-1}$ Mpc scale. The jointed constraint shows that
$\alpha$ = $ 0.000662_{- 0.000662}^{+ 0.000173}$ and $\sigma_8$ = $ 0.824_{-
0.0166}^{+ 0.0128}$. The CMB and matter power spectra are both similar for the
case of $\alpha=$ mean value and that of $\alpha=0$. However, the evolutionary
curves of $f\sigma_8(z)$ are different. This means that, to some extent, the
data points of the growth rate could break the degeneracy of the dark energy
models.
