A　pure　rocksalt　MgO　buffer　layer　was　used　to　modify　the　surface　structure　of　MgAl2O4　(1　1　1)　substrates　to　achieve　growth　of　a　Zn-polar　ZnO　film　by　radio　frequency　plasma-assisted　molecular　beam　epitaxy.　It　is　found　that　this　pure　rocksalt　MgO　buffer　layer　plays　a　crucial　role　in　30　degrees　rotation　domain　elimination,　surface　morphology　improvement　and　Zn-polarity　control　of　the　ZnO　film,　as　demonstrated　by　in　situ　reflection　high-energy　electron　diffraction　and　ex　situ　transmission　electron　microscopy.　Atomic　force　microscopy　observation　also　illustrates　a　smooth　surface　for　the　ZnO　film.