Under unsteady flow, the fatigue damage of the structure and the sediment carrying capacity of the water flow are greatly affected by the wake vortices generated by the flow around the cylinder. Based on the flume experiment of pile group around unsteady flow, the bottom flow velocity around the pile group was measured by acoustic Doppler velocimeter (ADV), and the influence and law of the flow around the pile group on the bottom flow field, transverse and longitudinal time average velocity distribution, transverse and longitudinal turbulence intensity were analyzed under the condition of single peak flood type unsteady flow. The research has shown that the average flow velocity in both horizontal and vertical directions is correlated with changes in flow rate. The average flow velocity in vertical direction is positive, and the average flow velocity in horizontal direction is consistent at symmetrical measuring points on the left and right banks. The relative turbulence intensity of longitudinal velocity and transverse velocity is only related to the magnitude of flow rate, and is not related to the rising and falling stages of flow rate. The influence range of pile group flow on the nearby flow field is limited, and there are certain differences in the degree of influence of pile group flow in different regions.