Constructing　approximate　dual　frames　is　much　easier　than　constructing　classical　dual　frames,　and　approximate　dual　frames　derive　an　almost　same　perfect　reconstruction　formula　as　classical　dual　frames.　In　this　paper,　under　the　background　of　subspace　frames　(fusion　frames),　an　explicit　characterization　of　approximate　dual　g-frames　was　obtained.　As　an　application,　we　prove　that　for　a　given　pair　of　approximate　dual　g-frames　({Λn}n,　{Γn}n),　there　existed　another　pair　of　approximate　dual　g-frames　({Ψn}n,　{Υn}n)　such　that　TΛUΓ=TΨUΥ,　where　TY　and　UY　denote　the　pre-frame　and　analysis　operators　of　the　g-frame　{Yn}n.　©　2017,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.