In　this　paper,　we　propose　an　efficient　scheme　to　generate　the　N-atom　singlet　state　via　adiabatic　passage　of　a　dark　state　in　cavity　quantum　electrodynamics　(QED)　system.　Appropriate　Rabi　frequencies　of　the　classical　fields　are　selected　to　realize　the　present　scheme.　We　discuss　the　influence　of　decoherence　induced　by　cavity　decay　and　atomic　spontaneous　emission　by　numerical　calculation.　The　result　shows　that　the　scheme　is　insensitive　to　atomic　spontaneous　emission　as　the　atomic　excited　state　is　hardly　populated　in　adiabatic　evolution.