Understanding the variation in heat and mass transfer during mode switching of a unitized regenerative fuel cell is essential for designing efficient flow channels and operational strategies. In this study, dynamic variation of current density, temperature, and species distribution during mode switching is investigated in a unitized regenerative fuel cell with a stepped flow channel. This work is conducted by a transient multi-physics model coupled with electrochemical reaction, heat and mass transfer, and phase change. Results indicate that the response time of current and temperature is prolonged as the mode-switching frequency rises. Using stepped channels instead of conventional straight channels can promote mode-switching and shorten the response time. Specifically, the stepped structure promotes airflow disturbance in flow channels, and the induced forced convection promotes heat and mass transfer. Besides, the stepped structure accelerates the stabilization of current density, temperature, and species during mode switching, leading to a more uniform current density distribution. In addition, the stepped structure promotes water discharge and convective heat transfer, improving the temperature uniformity of the catalyst layer. This study offers valuable insights for improving the durability of the membrane electrodes and improving the operational stability of unitized regenerative fuel cells during mode switching.