  Using $e^{+}e^{-}$ annihilation data corresponding to a total integrated
luminosity of $6.32$ fb$^{-1}$ collected at the center-of-mass energies between
4.178 and 4.226 GeV with the BESIII detector, we perform an amplitude analysis
of the decay $D^+_s \to K^-K^+\pi^+\pi^+\pi^-$ and determine the relative
fractions and phases of different intermediate processes. Absolute branching
fraction of $D^+_s\to K^-K^+\pi^+\pi^+\pi^-$ decay is measured to be
($6.60\pm0.47_{\rm stat.}\pm0.35_{\rm syst.})\times 10^{-3}$. The dominant
intermediate process is $D_{s}^{+} \to a_1(1260)^+\phi, \phi\to K^-K^+,
a_1(1260)^+\to \rho\pi^+, \rho\to\pi^+\pi^-$, with a branching fraction of
$(5.16\pm0.41_{\rm stat.}\pm0.27_{\rm syst.})\times 10^{-3}$.
