In order to improve the performance of line spectrum detection,according to the feature that the underwater target radiated noise containing stable line spectrum,the differences of the phase difference between line spectrum and background noise,a weighted line spectrum detection algorithm based on the phase variance is proposed in frequency domain.After phase difference alignment,the phase variance of line spectrum and the phase of background noise,respectively,are small and big in frequency domain,this method utilizes the weighted statistical algorithm to cumulate the frequency spectrum based on the phase variance,which can restrain the background noise disturbance,and enhance the signal to noise ratio(SNR).The theory analysis and experimental results both verify that the proposed method can well enhance the energy of line spectrum,restrain the energy of background noise,and have better detection performance under lower SNR. In order to improve the performance of line spectrum detection, according to the feature that the underwater target radiated noise containing stable line spectrum, the differences of the phase difference between line spectrum and background noise, a weighted line spectrum detection algorithm based on the phase variance is proposed in frequency domain. After phase difference alignment, the phase variance of line spectrum and the phase of background noise, respectively, are small and big in frequency domain, this method utilizes the weighted statistical algorithm to cumulate the frequency spectrum based on the phase variance, which can restrain the background noise disturbance, and enhance the signal to noise ratio (SNR). The theory analysis and experimental results both verify that the proposed method can well enhance the energy of line spectrum, restrain the energy of background noise, and have better detection performance under lower SNR.