Casing instantaneous pressure measurements and full-annulus unsteady simulations were undertaken to analyze flow characteristics near casing at stable and stall inception conditions in an axial flow compressor rotor, and the objective was to establish its linkage with the stall inception process. The measured flow characteristic at near-stall stable operating conditions was the appearance of rotating instability (RI), which attributed to the activity of an unsteady flow with varying frequency. A similar flow characteristic was found in the simulated near-stall stable flow conditions, and detailed analyses of instantaneous flow field indicated the formation and activity of tip secondary vortex could be flow mechanism for the appearance of RI as far as nonuniform tip loading distribution in measurements was concerned. The measured flow characteristic before spike emergence was still the activity of RI. However, it was submerged into flow field accompany by the emergence of spike. The simulated stall inception process was similar to that from measurement, and further analyses of instantaneous flow field established the causal linkage between RI and stall inception process for the test rotor.