Abstract: Research purposes: As the general representation of random track irregularity geometrical state，the power spectral density (PSD) of track irregularity is not only an effective approach to analyze and evaluate track smoothness, guide track maintenance and reparation, but also an important input excitation to design and assess the dynamical performance of vehicle, track, bridge and other structures. Corresponding study on track irregularity PSD is highly focused by the research and management organizations at home and abroad. Research conclusions ： ( 1 ) This paper reviews and summarizes the fitting formulas and their parameters, wavelength ranges, applicative speed classes of typical track irregularity PSDs at home and abroad in detail. On this basis, the shortcomings and problems that should be further researched for the study of track irregularity PSD in China are pointed out. (2) A thorough track irregularity PSD standard system can be built, through the complement of track irregularity PSD of typical railway lines and the extension of track irregularity PSD wavelength range, especially the short wavelength PSD of longitudinal level for high - speed railway. (3 ) Investigating the evolution law of track irregularity in the frequency domain and the corresponding PSD limit by means of track irregularity PSD, has significant engineering value for the maintenance of track geometry state and the rational formulation of track irregularity amplitude and PSD limits.