Because　of　the　Bragg　selectivity　of　volume　holographic　gratings,　it　helps　VHI　system　to　optically　segment　the　object　space.　In　this　paper,　properties　of　point-source　diffraction　imaging　in　terms　of　the　point-spread　function　(PSF)　are　investigated,　and　characteristics　of　depth　and　lateral　resolutions　in　a　VHI　system　is　numerically　simulated.　The　results　show　that　the　observed　diffracted　field　obviously　changes　with　the　displacement　in　the　z　direction,　and　is　nearly　unchanged　with　displacement　in　the　x　and　y　directions.　The　dependence　of　the　diffracted　imaging　field　on　the　z-displacement　provides　a　way　to　possess　3-D　image　by　VHI.　©　2009　SPIE.