Abstract: The flow field of straight HP turbine cascade was investigated experimentally in a large-scale low-speed open-loop cascade heat transfer wind tunnel.Three-dimensional flow fields near the endwall of the cascade were measured by using five-hole probe at five different Re .Cotton thread and floating small ball are applied to visualization of the flow fields.The experimental results show that the pressure side leg of the horseshoe vortex destroys the structure of the incoming flow boundary layer,when it moves from Pressure Side (PS) to Suction Side (SS).Behind the pressure side leg,a new boundary layer is generated near the endwall in the cascade.The new boundary layer goes from PS to SS.However,its thickness is thinner than that in the incoming flow.The 3D-flow region occupies 40% flow passage of turbine cascade.The increase of Re intensifies 3D-flow near endwall.From the photos of flow visualization it can be seen that corner vortex is generated and developed near the suction surface of blade/endwall junction,and forms a triangle region on the suction surface.The size of visualized passage vortex is consistent with measurement result.