Mode switching is an important process in unitized regenerative fuel cells. The complex interactions of heat and mass transfer during the operation of mode switching have a significant effect on cell performance. Twelve different ways of mode switching were proposed by controlling inlet boundary conditions of supplies and operating voltage. Numerical simulations were applied to analyze the dynamic response of heat and mass transfer as well as electrochemical signals under the different ways of mode switching. Current density increased with mass fraction of reactants. Cell heat source had an instant response to current density, but the temperature was slow to respond to the heat source. Hydrogen-side inlet velocity had minimal impact on mode switching. The time for cell reaching stability increased with the increase of voltage change time, and the time for current density, mass transfer, and temperature reaching stable values increased in order. Unitized regenerative fuel cell had similar dynamic response in the 2 period: cell temperature increased in the fuel cell mode and decreased in the water electrolysis mode after mode switching.