Abstract: Detailed measurements of three dimensional mean flow field at both inlet and exit of an isolated axial flow compressor rotor passage were made in different mass flow conditions.The flow structure was surveyed with a conical four hole high frequency response pressure probe.Strong periodic circumferential distributions of flow parameters were found at inlet of the rotor passage,especially in near stall condition.Both total pressure and static pressure are higher near the blade pressure surface,but lower near the suction surface.Lower axial velocity and larger relative flow angle appeared near the leading edge.The investigation shows that in design condition,mixing between the tip leakage vortex and the endwall boundary layer are main factors of the substantial blockage and loss in the tip mid passage;as the mass flow reduces,the enhanced leakage vortex produces more flow blockage and loss,and a vortex appears at the corner between the suction surface and the casing wall;while the intensified tangential migration in the hub wall boundary layer enlarges flow blockage and loss.In near stall condition,interaction among the tip corner vortex,the leakage vortex and the endwall boundary layer deteriorates the flow and leads to larger blockage and loss,and flow separation of the boundary layer on the suction surface occurs at 0.2 span and 0.8 span respectively.