The　digital　holographic　method　is　used　to　characterize　the　phase　modulation　depth　of　phase-only　LCOS.　Compared　with　the　conventional　ways,　the　digital　holographic　method　could　obtain　the　information　around　the　whole　field　of　view.　Besides,　the　digital　holographic　method　is　a　non-contact,　lossless,　high-fidelity　way　to　achieve　the　phase　distribution.　In　this　paper,　the　lensless　Fourier　transform　digital　holography　is　employed,　due　to　its　simple　setup　and　reconstruction　process.　In　LCOS　the　phase　modulation　is　controlled　by　displaying　the　gray　level　images　on　its　active　area.　Usually　for　the　phase　modulation　characterization,　the　total　of　all　255　gray　level　images　are　displayed　in　a　step　change　of　10,　for　each　recording.　That　is　why　it　takes　time　for　the　complete　calibration.　In　this　method　a　mask　with　the　entire　range　of　gray-level　i.e.　from　0-255　is　displayed　on　the　LCOS　active　area　and　the　hologram　is　recorded,　which　on　reconstruction　gives　the　depth　of　phase　modulation　of　LCOS　for　the　entire　range　of　gray　level.　In　order　to　avoid　the　aberration　a　double　exposure　method　is　used　in　which　two　holograms　are　recorded,　one　with　the　0-255　and　other　with　the　zero　gray　level　masks.　Also,　the　sorting　by　reliability,　following　a　non-continuous　path　(SNRCP)　phase　unwrapping　algorithm　is　used　for　unwrapping　the　final　result.　The　main　advantages　of　this　method　are　the　less　number　of　required　recording　holograms,　the　easy　and　real　time　calibration.　Results　are　then　compared　with　the　conventional　method　that　is　young　double　slit　method,　which　is　widely　proposed　to　obtain　the　phase　modulation　depth　of　the　LCOS　and　they　are　in　good　agreement　with　each　other.　The　efficiency　of　our　method　is　verified　by　comparison.