Due to the chromatic dispersion of the traveling wave in the transmission line, it is difficult to calcu- late the wave velocity accurately by use of the traveling wave fault location device. And the accuracy of the lo- cation would be affected too. The chromatic dispersion of the traveling wave is mainly caused by the frequency dependent character of the line impedance. Different from other guide lines, the steel rail in the traction network has its specificity. In this paper, the magnetic characteristic of the steel rail was tested by using the ballistic method from magnetic property detection of soft magnetic materials. The accurate magnetic characteristic data were obtained, including P60 steel rail fundamental magnetization curve, hysteresis loop and coercivity, etc. With the help of these data, the finite element simulation software was adopted to calculate the accurate frequency- dependent parameters of the impedance. On this basis, the traction network impedance and the frequency-de- pendent parameter matrix of the admittance were calculated by the parallel multi-conductor transmission line theory, while the special ferromagnetic characteristic of the steel rail was well-considered. It provides calculation scheme and the data foundation of the line impedance for the study of the traveling wave fault location of trac- tion network.