Abstract: In passive sonar,the noise normalization is usually implemented along frequency axis or azimuth axis.In order to improve the performance of the multi-beam narrowband detection,a new normalization technique needs to be taken for estimating the mean of noise.Because line frequency spectrum of radiated noise could leak into adjacent beams,a multi-stage normalization method is applied to passive narrowband detection.According to a selected window,noise normalization is implemented along frequency axis and azimuth axis of multi-beam LOFAR pictogram.This method can suppress leakage of line frequency spectrum among the adjacent beams and improve the detection performance of multi-beam LOFAR processing effectively.The results of sea-trial data processing show that the new noise normalization technique is effective.