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The complex vortex structure compressor leads to the problem that the transition model is insufficient in predicting the flow instability of the compressor. In this paper, the rectangular cascade of compressor of different turning-angle conditions is taken as the object, and the transition characteristics on the end wall and the blade surface of the compressor cascade are in comparison by the method of large eddy simulation/LES. The effects of the horseshoe vortex and the separation bubble over the compressor cascade on the transition process are emphatically discussed. By analyzing characteristic parameters of the vortex structure, it is found that the separated transitional flow corresponds to multiple separations-and reattachments of the shedding vortex, and is affected by the cross-flow transition and the separate-transition. Finally, by discussing the instability of the separation line, reattachment line and the cross-flow inflection point of the separated transitional flow, it reveals that the transient disturbance caused by the vortex motion is an important reason affecting the prediction accuracy of the transition model.