While　experimental　evidence　demonstrates　that　the　presence　of　hydrogen　(H)　impurities　in　diamond　films　plays　a　significant　role　in　determining　their　physical　properties,　the　small　radius　of　the　H　atom　makes　detecting　such　impurities　quite　a　challenging　task.　In　the　present　work,　first-principles　calculations　were　employed　to　provide　an　insight　into　the　effects　of　the　interstitial　hydrogen　on　the　electrical　and　mechanical　properties　of　diamond　crystals　at　the　atomic　level.　The　migrated　pathways　of　the　interstitial　hydrogen　are　dictated　by　energetic　considerations.　Some　new　electronic　states　are　formed　near　the　Fermi　level.　The　interstitial　hydrogen　markedly　narrows　the　bandgap　of　the　diamond　and　weakens　the　diamond　crystal.　The　obvious　decrement　of　the　critical　strain　clearly　implies　the　presence　of　an　H-induced　embrittlement　effect.