Fresnel　incoherent　correlation　holography　(FINCH)　is　one　of　the　methods　for　recording　holograms　of　3D　samples　under　incoherent　illumination.　The　FINCH　combines　the　theory　of　spatial　self-coherence　and　the　in-line　phase-shift　technology　together　to　form　a　complex　hologram.　A　spatial　phase　light　modulator　(SPLM)　plays　important　roles　as　the　dynamic　diffraction　optical　element　(DOE)　and　phase　shifter.　When　the　incoherent　light　generated　from　each　object　point　of　the　3D　samples　incidents　to　a　SPLM,　it　can　be　split　into　two　spatial　self-coherent　beams　with　different　curvatures.　The　hologram　caused　by　these　two　beams　can　then　be　captured　by　an　image　detector.　Three　holograms　with　different　phase　shift　are　recorded　sequentially　for　eliminating　the　zero-order　and　twin　image,　and　then　a　complex　valued　hologram　is　obtained　by　superposing　the　three　holograms.　In　this　paper,　the　modulation　characteristics　of　SPLM　and　phase　shift　error　in　FINCH　are　investigated.　Based　on　digital　holography,　phase　modulation　characteristics　of　SPLM　are　measured　under　coherent　and　narrow-bandwidth　incoherent　illumination　respectively.　Phase　shift　error　due　to　quasi　monochromatic　light　illumination　is　then　analyzed　in　FINCH.　The　effect　of　phase　shift　error　on　the　quality　of　reconstructed　image　is　also　investigated.　It　is　demonstrated　the　FINCH　setup　has　a　smaller　phase　shift　error　by　experiment.