In order to study the impact of the flood process on groundwater in a riparian zone, laboratory experiments and numerical simulations were conducted to investigate the groundwater level fluctuation subjected to floods with different amplitudes and durations. The results show that the groundwater level fluctuation was asymmetric, that groundwater rose quickly and declined slowly. The amplitude of the groundwater level fluctuation attenuated with an exponential trend and a significant time lag as the distance from the bank increased. As the flood amplitude increased, the groundwater level fluctuation was enhanced, resulting in an increased amount of exchange between the river water and groundwater. However, the time lag with respect to the groundwater level changed slightly. As the duration of flood peaks increased, the time lag was significantly enhanced, the groundwater level fluctuated more significantly, and it took more time for the groundwater level to return to the pre-flood status.