The quality of railway track geometry has a critical influence on the safety and comfort of train operations. In order to assess track geometry quality more effectively, the factor of track geometry wavelength should be considered. In this paper, a novel approach of assessment of track geometry quality based on intrinsic mode function (IMF), which derived from the measured data of track geometry by their characteristic wavelength scales, is presented. For this purpose, the frequency spectrum and the energy of each IMF of track geometry are calculated via fast Fourier transform method. The energy coefficient of each IMF of track geometry is defined as the ratio of each energy of IMFs to the total energy of the track geometry, and then the new parameter index is obtained with the corresponding calculation. In comparison with Track Quality Index (TQI) which is the main management method of track geometry in China, the new approach has been proved to be a general form of TQI. Finally, the track geometry data collected by track recording vehicles from Hefei-Wuhan high speed railway is studied using the new parameter index. The statistic analyzing results indicate that the new parameter index is the development and extension of Track Quality Index and can assess the track quality accurately and effectively.