Corrosion of carbon steel in soil would occur under the action of alternate current

which changes the condition of grounding system and harms safe operation of the electrical appliances.To reveal the current distribution characteristics of earth wires on extra-high voltage HGIS（hybrid gas insulated substation） enclosure and analyze the current effect on corrosion of the grounding body

a current distribution model of the earth wire is built in this paper.And the effectiveness and correctness of the model are verified by a large number of test data and statistical analysis.Ultimately

the effects of different current density on the carbon steel corrosion are obtained through tests

and the relationship between the current density and corrosion rate is fitted.This research demonstrates that:（1）The distribution shape of the current in the earth wire is similar to the oscillation waveform without unique distribution law;（2）There exists positive correlation between the current in first earth wire and last earth wire and the load current at the same phase

while the distribution law of the currents in the earth wires at other places is not obvious;（3）There is a proportional factor k between load current and earth wire current with the value in the range of 10 to 30 for most cases

and the corrosion rate range of carbon steel grounding system can be calculated with k and load current;（4） The larger the current density is

the heavier the carbon steel corrodes

and the corrosion rate is close to saturation with current density increasing.