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The acoustic performance test of a helicopter rotor model is one of the most effective and direct way to study the helicopter rotor noise features. In an acoustic test of a helicopter rotor model in the anechoic chamber,it is found that unwanted wideband noises have superimposed on the rotor acoustic signals which are distributed around the 170Hz characteristic frequency in an extremely narrow band. Since the signal to noise ratio (SNR) is proportional to the collective pitch,when the collective pitch is small,a low SNR will lead to real information of the signal be covered by the unwanted signal components. It is necessary to find a way to remove the unwanted components and to remain intact wanted components. Different components of the acquired acoustic signal have different frequency band distributions,and the signal autocorrelation length relies on its frequency band distribution,so in this paper,it points out that the required signal components can be separated using the adaptive linear predictor according to the differences of the autocorrelation length of the components of the signals. The results of the processing of the acquired signals when the collective pitch are 0°、6°、10°respectively show that noises are filtered successfully and the signals are improved significantly.