To investigate the structure and the unsteady flow characteristics of the tip vortices under near stall condition of a compressor cascade with clearance, the large eddy simulation (LED) method is conducted with NACA64A905 cascade to explore the structure characteristics, the flow pattern and the coupling process of the tip vortices with Q criteria. It is found that compared with the rated condition, the tip flow field in the near stall condition is more complicated. The existence of secondary tip leakage vortex is found by LES. Tip leakage vortex does not breakup under the rated condition while the main and the secondary tip leakage vortex will breakup in the near stall condition, and the lowenergy fluid caused by the breakup of tip leakage vortices and the trailing separation vortex are the main causes of tip blocking and loss. The secondary tip leakage vortex′s forming point and the angle with chord are periodically changed in different time, and this together with the periodic shedding of corner separation vortex are the main reasons of the unsteady tip flow.