  We present the first amplitude analysis of the decay $D_s^+\to
K^-K^+\pi^+\pi^0$ using data samples of 6.32 fb$^{-1}$ recorded with the BESIII
detector between 4.178 and 4.226 GeV. More than 3000 events selected with a
purity of 97.5\% are used to perform the amplitude analysis, and nine
components are found necessary to describe the data. Relative fractions and
phases of the intermediate decays are determined. With the detection efficiency
determined by the results of the amplitude analysis, we measure the branching
fraction of $D_s^+\to K^-K^+\pi^+\pi^0$ decay to be $(5.42\pm0.10_{\rm
stat.}\pm0.17_{\rm syst.})\%$.
