To understand the change of electric field strength around high-speed railway under the effect of lightning downward leader and further reveal the lightning mechanism of high-speed railway

leader progression model is adapted to build a three-dimensional lightning strike model.By adjusting the charge

height and lateral distance of the conductor

the effects of lightning current amplitude and progression of downward leader nearby the earth on the electric field strength distribution around high-speed railway are simulated

and the electric field strength distribution in viaduct section is compared with that in rail-bed section.Results show that upward leader still occurs around high-speed railway while the amplitude of lightning current is several kiloamperes.It is proposed that upward leader should be considered even under little lightning current in lightning calculation.Research finds that lightning wire generates upward leader easier than the other conductors while adjusting the space location of downward leader and changing amplitude of lightning current.And it finds that electric field strength of viaduct section is 40% higher than that of roadbed section

so lightning protection designation and construction requirement of high-speed railway in viaduct section should be higher than that in roadbed section.