A　unitized　regenerative　fuel　cell　is　a　typical　gas　liquid　two-phase　system　that　consumes　oxygen　and　hydrogen　in　a　fuel　cell　mode　and　liquid　water　in　an　electrolytic　cell　mode.　Liquid　water　removal　is　crucial　for　a　successful　cell　start-up　after　the　electrolytic　cell　mode　ends.　However,　investigations　on　two-phase　transfer　mechanisms　for　liquid　water　removal　are　limited　during　mode　switching.　To　fill　this　research　gap,　a　three-dimensional　two-phase　full-cell　model　is　developed　to　describe　charges,　gas　mixtures　and　liquid　water　transfer　corresponding　to　operational　modes　of　electrolytic　cell,　gas　purging　and　fuel　cell.　The　cell　is　assumed　to　being　in　the　isothermal　state.　Numerical　model　is　analyzed　by　using　COMSOL　Multiphysics　5.3a　software.　Furthermore,　experimental　and　simulated　results　are　compared　to　validate　the　proposed　model.　Results　show　that　more　than　84.0%　of　pore　volume　is　occupied　with　liquid　water　on　porous　layers　in　an　electrolytic　cell　mode.　Although　pre-switching　for　water　removal　can　decrease　the　volume　fraction　of　liquid　water　within　the　porous　layers　from　0.88　to　0.50　in　a　short　time,　more　time　is　required　for　liquid　water　being　carried　away　under　a　low　level　of　water　flooding.　Purging　result　presents　diverse　influences　on　start-up　performance　in　a　fuel　cell　mode.　Liquid　water　distribution,　which　is　similar　to　that　in　a　fuel　cell　mode,　formed　in　a　purging　mode　is　encouraged　for　promoting　a　quick　and　stable　start-up　in　a　fuel　cell　mode.