Research conclusions: The maximum traction 10ad of section post arises under the conditions that the fleet trains run in the heavy—duty direction and no train runs in the light—duty direction．Both the maximum 10ad current and the maximum equivalent current in the section post increase linearly with the increase of train quantity．The max．Equivalent current of the section post can be taken approximately by 30％of the total current separately feeding to the up and down tracks at the first end in the heavy—duty direction when there is less fleet train and call be taken by quarter when there is much fleet train．