The　GPB-II　zone　is　the　main　strengthening　precipitate　in　the　Al-4.5Zn-1.5Mg-1.0Cu-0.35Si　(wt.%)　crossover　alloy,　resulting　in　increased　alloy　strength　and　ductility.　The　atomic　structure　of　the　GPB-II　zone　and　its　evolution　process　during　aging　have　been　studied　by　high-angle　annular　dark-field　scanning　transmission　electron　microscopy　(HAADF-STEM)　in　the　present　work.　It　is　shown　that　the　GPB-II　zone　is　a　hybrid　precipitate　consisting　of　the　L　phase　(a　disordered　phase　with　a　QP　lattice　and　is　normally　present　in　Al-Mg-Si-Cu　alloy)　on　the　inner　part　and　Guinier-Preston-Bagaryatsky　(GPB)　zones　(an　important　strengthening　phase　in　Al-Cu-Mg　alloy)　on　the　outer　part.　The　GPB-II　zone　is　formed　by　the　GPB　zone　nucleating　at　the　Cu　site　(in-between　and　on　the　Sinetwork)　of　the　L　phase.　The　unique　combination　of　the　GPB　zone　and　L　phase　was　investigated,　and　the　＂Si　parallelogram　embedding　with　Cu＂　was　proposed.　The　GPB　zone　provides　the　atoms　for　the　L　phase＇s　growth　and　results　in　the　coarsening　of　the　L　phase　with　few　GPB　zones　after　a　long　aging　time.　The　role　of　the　Zn　element　in　the　formation　of　the　GPB-II　zone　was　discussed.　It　is　thought　to　have　a　similar　effect　as　Cu　and　can　also　promote　the　formation　of　GPB　zones　on　the　L　phase.