Abstract: Line spectra provide significant information in ship-radiated noise. Extracting spectral lines from ship-radiated noise is a key technique in identification of underwater targets. In this paper the physical causes and spectral characteristics of ship-radiated noise are first briefly introduced. Based on simulation of line spectral estimation with MATLAB, a unified analysis method is provided to estimate the spectral lines in ship-radiated noise ranging from DC to 100Hz using the periodographic method and modern spectrum estimation method for short-time series. The ship-radiated noise signals from two ships are analyzed by using the proposed method. A characteristic spectral line at 5.25Hz is found from a ship of type A moving at a medium speed, and characteristic spectral lines at 65.5Hz and 69.2Hz respectively are found from a ship of type B. The results show that the described method is effective in extracting spectral lines from ship-radiated noise.