Abstract: Secondary flow is one of the typical characteristics of flow movement in curved bends, which are divided into two categories. The first type is caused by the difference of radial differential pressure acting on the fluid when flowing through the elbow. The second is mainly caused by turbulent anisotropy. Although the velocity of this type is relatively small, it is closely related to the bank erosion process. However, the research in recent years has paid less attention to the evolution process of the second type of secondary flow. Therefore, this study uses high-precision three-dimensional velocity data to investigate the secondary flow structure and its dynamic characteristics, especially the evolution process of the second type of secondary flow. The results show that: for sharp bend flow with high Reynolds number, multiple circulation often occurs in bend flow due to obvious turbulence anisotropy; for longitudinal velocity, when water flows through the apex of the bend, the distribution of longitudinal velocity along the vertical direction significantly deviates from the logarithmic velocity distribution; when water flows through the apex of the bend, there is an obvious trend of uniformity along the vertical line of longitudinal flow velocity; when the Froud number is large, the large-scale vortices continue to decompose, reducing the influence of the original anisotropy; the small-scale vortices near the concave bank tend to be isotropic, causing the small vortices to gradually weaken and eventually disappear; the interaction between secondary flow and longitudinal flow is significant in sharp bends; and the secondary flow redistributes momentum within the section and carries some high-speed fluid to other regions of the section. Therefore, in the area where the secondary flow occurs, the longitudinal flow velocity is generally smaller.