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Recently XENON1T Collaboration announced that they observed some excess inthe electron recoil energy around a 2-3 keV. We show that this excess can beinterpreted as exothermic scattering of excited dark matter (XDM), $XDM +e_{atomic} \rightarrow DM + e_{free}$ on atomic electron through dark photonexchange. We consider DM models with local dark $U(1)$ gauge symmetry that isspontaneously broken into its $Z_2$ subgroup by Krauss-Wilczek mechanism. Inorder to explain the XENON1T excess with the correct DM thermal relic densitywithin freeze-out scenario, all the particles in the dark sector should belight enough, namely $\sim O(100)$ MeV for scalar DM and $\sim O(1-10)$ MeV forfermion DM cases. And even lighter dark Higgs $\phi$ plays an important role inthe DM relic density calculation: $X X^\dagger \rightarrow Z' \phi$ for scalarDM ($X$) and $\chi \bar{\chi} \rightarrow \phi \phi$for fermion DM ($\chi$)assuming $m_{Z'} > m_\chi$. Both of them are in the $p$-wave annihilation, andone can easily evade stringent bounds from Planck data on CMB on the $s$-waveannihilations, assuming other dangerous $s$-wave annihilations arekinematically forbidden.

XENON1T excess in local $Z_2$ DM models with light dark sector