Objective: This study addresses the challenges in experimental measurement and mechanism analysis of tip leakage flow (TLF) in rotating impellers by developing an advanced particle image velocimetry (PIV) methodology. The proposed methodology integrates a fully transparent shroud, equidistant chord-length measurement sections, and phase-locked rotational synchronization to achieve high-resolution visualization and quantification of TLF dynamics in a mixed flow pump. Methods: A comprehensive experimental platform was established at the State Key Laboratory of Hydroscience and Engineering, Tsinghua University; this included a closed-loop hydraulic test rig and a high-precision PIV system. The mixed flow pump used for testing featured a specific speed of 484, five-blade impeller, six-blade guide vane, and diameters of 150 mm at the inlet and 180 mm at the outlet. The PIV system features a 30-W laser with a 532-nm wavelength, a FASTCAM NOVA S12 high-speed camera, and SiO₂ tracer particles ranging in size from 10 to 50 μm. This setup achieved a spatial measurement resolution of 20 μm. Six equidistant chord-length sections (0, 0.2C, 0.4C, 0.6C, 0.8C, and 1.0C) along the blade chord direction were selected for analysis under three flow conditions: part-load (0.8Q_d), rated (1.0Q_d), and over-load (1.2Q_d), where Q_d = 34.5 kg/s. A phase-locked synchronization technique ensured repeatability for all measurements, maintaining a phase error of less than 1° and a temporal resolution of 0.115 ms. Post-processing of the datasets was conducted with SM-MICROVEC software, which utilized Gaussian filtering and AI-enhanced algorithms to calculate velocity and vorticity distributions. This approach enabled detailed measurement of the velocity fields, vorticity patterns, and vortex structures along the six sections. Results: The results show that relative velocity increased with higher flow rates, aligning with the blade profile direction at 1.0Q_d, validating the hydraulic design. Axial velocity rose with increasing flow rates but exhibited significant non-uniformity owing to the presence of low-velocity zones created by TLF near the suction surface. These zones migrated downstream, deviating from the blade's trailing edge. Absolute velocity reached its highest values at the mid-blade region but showed notable reductions near the tip, where interactions between tip leakage vortex (TLV) and wall shear forces dominated. TLV formed via shear interaction between TLF and mainstream flow. The area and vorticity intensity of the TLV exhibited a "rise-then-decline" trend along the blade chord, starting at the leading edge (0) and extending to the trailing edge (1.0C). TLV area peaks shifted downstream with increasing flow: 0.3C (0.8Q_d), 0.6C (1.0Q_d), and 0.8C (1.2Q_d). Vorticity peaks concentrated at 0.4C-0.6C across all conditions. At 1.0Q_d, the TLV occupies about 50% of the flow path at 0.6C and extends toward the hub at 1.0C. As the flow velocity increases, the separation vortex near the shroud inlet shrinks in the direction of increasing radius. The TLV interacts with these structures at 0.8Q_d but remains isolated at 1.0Q_d and 1.2Q_d. Ω standard analysis (Ω=0.52) shows structures associated with TLVs that vary in position with flow rate and string length, extending from the shroud to the midspan of the hub at 1.0Q_d. Conclusions: The proposed PIV methodology effectively resolves TLF characteristics in rotating machinery. The integration of a transparent shroud and phase-locked PIV system enables detailed quantification of TLF spatiotemporal evolution. TLF significantly disrupts axial velocity uniformity, forming downstream-propagating low-speed zones. TLV dynamics correlate strongly with flow rate, with peak intensity and spatial influence varying along the blade chord. These insights provide critical data for optimizing mixed-flow pump designs, aiming to mitigate energy losses and hydrodynamic instabilities induced by TLF.