Abstract: River connectivity, a fundamental property of river ecosystem, is affected by human activities as well as seasonal differences. A one-dimensional river network mathematical model was established to evaluate the impact of riverbed evolution and fluvial-tidal dynamics change on river connectivity during flood season in the lower reaches of Dongjiang River from Boluo to Shilong and Dongjiang River Delta (DRD) from 1999 to 2009. The results show that the loopiness of the study area was low, the linking sharing index was high and node connection rate was greater than 1, which indicated a relatively high topological connectivity. Noticed that the topological connectivity did not change with the uneven riverbed downcutting and fluvial-tidal variation. However, the dynamic connectivity has changed significantly with the uneven riverbed downcutting and fluvial-tidal variation. Due to the riverbed downcutting, fluvial dynamics decreased and tidal dynamics increased, with the decrease in the water conveyance capacity and dynamic connectivity of the study area. The results obtained from this study provides scientific supports for the research on water security such as flood control, water conservancy project planning and water ecological environment in the DRD.