The track irregularity which is the main vibrating resource of the vehicles and one of the main factors to limit the train highest speed, plays a very important part in the safety, stabilization and comfort of the trains. The statistic samples used by this paper are collected by track geometry inspection car from Qin-shen special line for passenger transport. Based on the stationary character test of the samples, FFT method was used to evaluate the spectrum of the statistical sample space, and MATLAB soft was used to get the PSD(power spectral sensity) of track irregularities. Based on statistical average of the samples of the track irregularities, frequency smoothing of the PSD and coupare with PSD of the main-line of Chinese railway were made. The curve to the PSD was fit. Then the track state of Qin+shen special line for passenger transport was evaluated.