Since　the　prediction　of　multi-hydrogen　high-temperature　superconductor　by　Ashcroft　in　2004,　many　possible　candidates　have　been　proposed,　e.g.,　LaH10　showing　the　highest　superconducting　transition　temperature　(T-c)　around　250-260　K　at　170-200　GPa　hitherto.　However,　this　pressure　is　too　large　to　be　taken　into　practical　use.　To　address　this　challenge,　it　proposes　a　few-hydrogen　metal-bonded　perovskite　superconductor,　MgHCu3,　by　combining　a　novel　design　idea　with　first-principles　calculations.　Different　from　multi-hydrogen　hydrides,　whose　high　T-c　relies　on　extreme　pressure,　the　metallic　bond　in　few-hydrogen　superconductor　MgHCu3　improves　the　structural　stability　and　ductility　at　atmospheric　pressure.　Here,　the　small　amount　of　hydrogen　is　found　to　be　vital　for　T-c.　After　the　incorporation　of　hydrogen,　the　electron-phonon　coupling　constant　of　MgHCu3　is　increased　to　0.83,　which　is　larger　than　that　of　the　well-known　MgB2.　Moreover,　the　anisotropy　of　MgHCu3　also　plays　an　important　role　in　enhancing　T-c.　Based　on　the　Migdal-Eliashberg　theory,　it　predicts　that　the　phonon-mediated　metal-bonded　perovskite　MgHCu3　is　a　superconductor　with　T-c　of　42　K.　The　first　predicted　ternary　metal-bonded　perovskite,　MgHCu3,　enriches　the　family　of　perovskite　and　will　promote　further　investigation　on　few-hydrogen　superconductors　under　atmospheric　pressure.