An experiment was carried out in a low-speed large-scale axial-compressor. Dynamic pressure signals were measured and analyzed with a wavelet transform. At all stable operating condition, a shaft order perturbation was observed from the dynamic pressure signals and wavelet power spectrums. By measuring the tip clearance, blade pitches and blade thickness distributions, a rotor asymmetry was identified in this compressor, which is strongly linked to the shaft order perturbation. Modal wave appears at the near-stall operating point. The propagation speed of the modal wave is about 20% rotating speed. At the peak of the modal wave, the intensity of the shaft-order-perturbation increases obviously, while it decays very fast at the trough of modal wave. By throttling the compressor, modal stall occurs in several seconds and only one stall-cell was detected. The stall cell grows smoothly out of the modal wave and its propagation speed is increased to 30% rotor speed. In several revolutions before stall, the intensity of the modal wave is increasing and a shaft order perturbation produced by modal-wave grows into stall inception which indicate stall onset but not trigger stall. An experiment was carried out in a low-speed large-scale axial-compressor. Dynamic pressure signals were measured and analyzed with a wavelet transform. At all stable operating conditions, a shaft order perturbation was observed from the dynamic pressure signals and wavelet power spectrums . By measuring the tip clearance, blade pitches and blade thickness distributions, a rotor asymmetry was identified in this compressor, which is strongly linked to the shaft order perturbation. Modal wave appears at the near-stall operating point. The propagation speed of the modal At the peak of the modal wave, the intensity of the shaft-order-perturbation increases obviously, while it decays very fast at the trough of modal wave. By throttling the compressor, modal stall occurs in several seconds and only one stall-cell was detected. The stall cell grows smoothly out of the modal wave and its Propagation speed is increased to 30% rotor speed. In several revolutions b efore stall, the intensity of the modal wave is increasing and a shaft order perturbation produced by modal-wave grows into stall inception which indicate stall onset but not trigger stall.