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The long-standing Galactic center gamma-ray excess could be explained by GeV dark matter (DM) anni-hilation,but the DM interpretation seems to conflict with recent joint limits from different astronomical scale obser-vations such as dwarf spheroidal galaxies,the Milky Way halo,and galaxy groups/clusters.Motivated by 8Be and 4He anomalous transitions with possible new interactions mediated by a vector boson X,we consider a small frac-tion of DM mainly annihilating into a pair of on-shell vector bosons XX followed by X → e+e-in this paper.The Galactic center gamma-ray excess is explained by this DM cascade annihilation.The gamma rays are mainly from inverse Compton scattering emission,and the DM cascade annihilation could be compatible with joint astrophysical limits and meanwhile be allowed by AMS-02 positron observation.The direct detection of this model is also dis-cussed.