This study investigates the model of structural steels used in the lightning current analysis. These steels, magnetic material, can be found in grounded structures, such as towers and buildings. An equivalent electrical circuit is presented first for these magnetic conductors under lighting transient current. Circuit parameters of the steel wires are determined numerically with an equivalent circuit approach. A rational function approximation is incorporated for developing an extended circuit model of frequency-dependent circuits used in time-domain simulations. Experiments are carried out to disclose the transient response of both steel bars and rods when they carry a surge current directly. It is found that these steel wires exhibit weak ferromagnetism, and can be represented with linear magnetic materials. The proposed modelling procedure is applied to analyse surge current sharing in a three-dimensional steel wire/power cable system adopted in radio base stations. Good agreements with the experimental results are observed.