The　inherited　coherent　noise　degrades　the　phase　imaging　quality　in　digital　holographic　microscopy　(DHM).　To　overcome　the　problem,　an　experimental　investigation　on　the　three-dimensional　(3D)　spatial　correlation　properties　of　coherent　noise　is　carried　out.　Multiple　blank　holograms　are　recorded　without　any　specimen　in　DHM　setup　by　consecutively　shifting　camera　along　the　optical　axis,　and　a　series　of　phase　distribution　of　coherent　noise　can　be　obtained　by　numerical　reconstruction.　Then,　based　on　the　phase　distributions,　the　lateral　and　longitudinal　correlation　properties　of　coherent　noise　are　analyzed　by　a　discrete　correlation　algorithm.　Furthermore,　a　method　for　reducing　phase　noise　is　proposed　by　use　of　multiple　holograms.　Firstly,　a　series　of　holograms　are　recorded　by　shifting　the　camera　longitudinally　with　the　step　more　than　longitudinal　correlation　length　of　coherent　noise　field.　Secondly,　the　reconstruction　of　the　holograms　leads　to　a　series　of　phase　images　of　object,　in　which　the　coherent　noise　has　different　patterns.　Consequently,　by　averaging　the　phase　images,　the　reductions　of　phase　noise　are　achieved.　The　applicability　of　the　method　is　demonstrated　by　imaging　of　the　resolution　targets　and　the　grating.　Crown　Copyright　(C)　2013　Published　by　Elsevier　Ltd.　All　rights　reserved.