Abstract: It is very important to study internal flow characteristics of hydrodynamic coupling for its high efficient energy transmission. Consequently, it has great significance for us to study the internal flow mechanism and flow distribution of hydrodynamic coupling deeply. Based on this theoretical analysis, the cavity structure of hydrodynamic coupling can be further optimized, and it has great significance to enhance the performance of hydrodynamic coupling. A variety of flow structures and many physical effects will coexist in the internal flow field of hydrodynamic coupling, and there are many complex flow phenomena. Especially on braking condition, internal flow of turbine is a special kind of vortex flow. In order to study the generation and movement of vortex flow in the independent flow channel, flow images of radial cross-section in turbine was captured based on particle image velocimetry (PIV) technology. The large-scale vortices were identified by image processing techniques, including gray enhancement, threshold segmentation, edge detection and image sharpening. Based on this, the direction of flow velocity was identified and extracted clearly. The distributions of flow field were qualitative analyzed. The flow field and vorticity field were extracted through successive frames of image cross-correlation algorithm, and the small-scale vortices were discussed. The reasons of vortices generation and their impacts on energy transmission were analyzed. The development process of different scale vortices was discussed. The energy dissipation of flow was studied through distribution results of vorticity field. On the near-wall flow region of turbine, vortex flow was analyzed. Based on this, relative vorticity on the wall boundary region might have an important impact on the energy dissipation. The flow visualization of vortices and quantitative extraction of flow parameters were achieved by PIV technology and a valuable reference for the internal flow mechanism of hydrodynamic coupling was provided by PIV experimental results.