In　unitized　regenerative　fuel　cells,　residual　water　at　the　end　of　electrolysis　cell　mode　greatly　affects　the　cell　voltage　during　mode　switching　from　electrolysis　cell　to　fuel　cell　mode.　Therefore,　the　residual　water　removing　is　essential　to　realize　the　mode　switching,　which　requires　the　knowledge　on　gas　purge　effect　on　cell　voltage　dynamic　response.　In　this　study,　gas　purge　effect　in　oxygen　and　hydrogen　sides　on　cell　voltage　dynamic　response　is　investigated,　respectively.　In　addition,　the　effects　of　fuel　cell　mode　startup　current　density　and　electrolysis　cell　mode　operating　current　density　are　analyzed.　The　results　show　that:　the　increases　of　gas　purging　time　and　purging　gas　flow　rate　promote　the　mode　switching　from　electrolysis　cell　to　fuel　cell　modes.　High　flow　rate　of　purging　gas　is　preferred　than　long　gas　purging　time　during　mode　switching　when　the　same　amount　of　purging　gas　is　used.　In　addition,　gas　purging　in　hydrogen　side　is　necessary.　The　influence　of　residual　water　in　hydrogen　side　increases　with　the　startup　current　density　of　FC　mode,　and　long　purging　time　is　required　for　high　startup　current　density　of　FC　mode.　Electrolysis　cell　mode　operating　current　density　increase　leads　fuel　cell　mode　performance　decrease　under　the　same　gas　purge　condition.