Energy　conservation　is　a　long-term　strategic　approach　of　economic　development.　Subway　is　a　most　important　way　of　urban　mass　transit,　the　energy　consumption　of　subway　accounted　for　a　large　part　in　mass　transit.　Therefore,　retrofitting　the　subway　for　energy　saving　is　close　to　the　current　policy,　it　can　relieve　the　energy　pressure,　so　it　plays　an　important　role　on　the　sustainable　development　of　economy.　This　paper　conducted　a　survey　of　Beijing　subway　energy　consumption,　and　summed　up　annual　energy　consumption　data　of　the　Beijing　subway　lines.　Based　on　this　research,　this　paper　shows　the　energy-saving　potential　of　the　Beijing　subway.　Also　it　lays　the　foundation　of　energy　saving　transformation　for　subway.