A　pure-optical　quadratic　phase　compensationmethod　is　proposed　for　the　image-plane　digital　holographic　microscope.　Theoretical　analysis　testifies　that　the　quadratic　phase　can　be　removed　completely　only　when　the　reference　point　source　is　rightly　located　at　the　back　focal　plane　of　the　microscope　objective.　The　image-plane　digital　holographic　microscopy　is　built,　in　which　the　well　located　sphere　reference　beam　directly　emitting　from　the　tip　of　the　fiber　is　utilized　as　the　reference　beam.　Experimental　results　reveal　how　the　quadratic　phase　curvature　changes　with　the　scanning　of　the　reference　point　source,　and　make　the　adjustment　of　the　reference　beam　visualized　and　operable.　The　effectiveness　of　the　proposed　method　is　demonstrated　by　the　quantitative　three-dimensional　measurement　of　a　microlens　array　and　the　morphological　monitoring　of　living　mouse　fibroblast　cells.　The　quadratic　phase　aberration　can　be　compensated　inherently　without　any　computation,　which　greatly　eases　the　computation　load　in　the　reconstruction　of　the　digital　hologram　and　helps　to　improve　the　real　time　of　imaging　system.　Besides,　the　adjustment　and　alignment　of　the　quadratic　phase　free　image-plane　digital　holographic　microscope　is　practicable　and　convenient.　©　The　Optical　Society　of　India　2014.