Research on characteristics of helicopter rotor blade tip vortex is one of the key elements for helicopter rotor aerodynamic characteristics research.To improve the understanding of the blade tip vortex characteristics under hovering status and grasp the flow mechanism accurately, the Bo-105 rotor model hover test of tip Mach number similarity is conducted in open test section of Φ5 m vertical wind tunnel.In the same time, the hovering rotor flow filed of different collective pitches is measured elaborately with the TR-PIV measurement system, and then the detailed flow field (32 frames/circle) of this rotor is obtained.Based on the reasonable methods of the judgment of vortex center, extraction of vortex core flow parameter and fit of the vortex core model, the test results is processed and analyzed elaborately, and the evolution and development of blade tip vortex under hovering status is uncovered.The research shows that TR-PIV can catch the vortex characteristics correctly, and it will contribute to the elaborate study of rotor flow filed; using the weighted average of vorticity to calculate vortex center, it can avoid influence of shift speed on position of vortex core, and position of the vortex core accurately; using the circulation-based method, it can calculate size of vortex core and max induced velocity more reliably, and the results show that vortex core radius increases slowly and vortex core max induced velocity slowly decreases with increasing wake age; during the evolution of tip vortex, different development stages have different n parameters.