Digital　holography　microscopy　has　been　widely　used　as　a　testing　technology　in　many　areas　for　the　ability　of　real-time　three-dimensional　imaging.　In　this　study　we　focus　on　understanding　the　system　imaging　mechanism　and　recording　capacity　of　the　off-axis　image　plane　digital　holography　(IPDH)　which　has　several　advantages.　Wigner　distribution　function　and　space-bandwidth　product　are　utilized　to　examine　the　minimum　requirement　for　the　recording　capacity　of　the　CCD　camera.　The　discussion　Provides　a　good　understanding　and　a　useful　guide　to　the　formation　of　practical　IPDH　systems.