Research conclusions: When the traction power network separately supplies the upward track and downward track of double—track electrified railway，the equivalent current of the feeding section for upward track(or downward track)is approximately equal to the product of the interval number and the average current of upward(or downward)train．When the traction power network parallel supplies the upward track and downward track，the equivalent current of the feeding section for upward track(or downward track)is approximately equal to the 3／4 equivalent current of the upward track (or downward track)when separately supplying and plus the 1／4 equivalent current of the downward track(or upward track)when supplying separately．The the current carrying capacity of feeding section cab be improved by adopting parallel supply．More improvement can be achieved with the increasing of the average current difference between upward track and downward track，and the current difference can be reduced by 1／4 under the condition of electric load of the track on single direction slope．The equivalent current of section post is related to the average current difference between trains running on upward track and downward track．The equivalent current of section post is the minimum when the current of upward train is equM to that of downward train．The equivalent current of section post is the maximum and approximately equal to the 1／4 equivalent current of train running on the track with power supply separately when there is no train on one track or the average current of train is equM to zero．