A 2D transient mathematical model is developed for regenerative solid oxide cells operated in both SOFC mode and SOEC mode. The steady state performance of the model is validated using experimental results of in-house prepared NiO-YSZ/YSZ/LSM cell under different operating temperatures. The model is employed to investigate complicated multi-physics processes during the transient process of mode switching. Simulation results indicate that the trend of internal parameter distributions, including H-2/O-2/H2O and ionic potentials, flip when the operating cell is switched from one mode to another. However, the electronic potential shows different behaviors. At H-2 electrode, electronic potential keeps at zero voltage level, while at O-2 electrode, it increases from a relatively low level in SOFC mode to a relatively high level in SOEC mode. Transient results also show that an overshooting phenomenon occurs for mass fraction distribution of water vapor at H-2 side when the operating cell switches from SOFC mode to SOEC mode. The mass fractions of O-2 and H-2 as well as charge (electrons and ions) potentials may quickly follow the operating mode changes without over-shootings. The simulation results facilitate the internal mechanism understanding for regenerative SOFCs. Published by Elsevier B.V.