Abstract: The shallow groundwater samples from the Yellow River Estuary in a complete tidal cycle were collected, in which the dynamic changes of bacterial community structure influenced by tidal action were analyzed by using high-throughput sequencing and real-time fluorescence quantitative PCR. It was found that in the early stage of rising tide, the composition of bacterial community changed significantly and the proportion of marine bacteria in the groundwater increased gradually, and then it reached a high level in the late stage of rising tide. The bacterial community composition gradually kept stable in the stage of ebb tide. The bacterial abundance was higher in the early stage of rising tide than that in the late stage of rising tide and ebb tide. The concentration of silicate in the groundwater was the key environmental factor to affect the structure and abundance of bacterial community (P<0.05). In conclusion, the tide action had significant impacts on the characteristics of microbial community in the shallow coastal groundwater.