Rotating instability(RI) characteristics of a single-stage low-speed compressor were analyzed. Based on the preliminary results of RI characteristics, flow cause and influence with different tip clearances and full passage numerical simulation, two flow field decomposition methods were applied to obtain the flow components, energy proportion and stability of RI modes. The computation results reveal that the first several modes account for a large proportion of energy, make major contributions to the flow field and have stronger stability. With the decrease of tip clearance, the energy and stability of RI modes decrease gradually, while blade rotating and its harmonics become the main components in macro flow field.