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We investigated the electronic structure of a layered perovskite oxyfluoride $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ru}{\mathrm{O}}_{3}{\mathrm{F}}_{2}$ thin film by hard x-ray photoemission spectroscopy (HAXPES) and soft x-ray absorption spectroscopy (XAS) as well as density functional theory (DFT)-based calculations. The core-level HAXPES spectra suggested that $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ru}{\mathrm{O}}_{3}{\mathrm{F}}_{2}$ is a Mott insulator. The DFT calculations described the total and site-projected density of states and the band dispersion for the optimized crystal structure of $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ru}{\mathrm{O}}_{3}{\mathrm{F}}_{2}$, predicting that $\mathrm{R}{\mathrm{u}}^{4+}$ takes a high-spin configuration of ${(xy)}^{\ensuremath{\uparrow}}{(yz,zx)}^{\ensuremath{\uparrow}\ensuremath{\uparrow}}{(3{z}^{2}\ensuremath{-}{r}^{2})}^{\ensuremath{\uparrow}}$ and that $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ru}{\mathrm{O}}_{3}{\mathrm{F}}_{2}$ has an indirect band gap of 0.7 eV with minima at the $M,A$ and $X,R$ points. HAXPES spectra near the Fermi level and the angular-dependent O $1s$ XAS spectra of the $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ru}{\mathrm{O}}_{3}{\mathrm{F}}_{2}$ thin film, corresponding to the valence band and conduction band density of states, respectively, were drastically different compared to those of the $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ru}{\mathrm{O}}_{4}$ film, suggesting that the changes in the electronic states were mainly driven by the substitution of an oxygen atom coordinated to Ru by fluorine and subsequent modification of the crystal field.