Research　purposes:　To　investigate　the　formation　mechanism　and　mechanical　characteristics　of　soil　arching　effect　within　pile　net　structure　in　embankment　under　train　load,　discrete　element　model　of　pile　net　structure　is　found　by　PFC3D　software　for　mesoscopic　research,　the　chain　of　contact　force,　the　horizontal　and　vertical　displacement,　and　vertical　distribution　of　soil　particles　stress　are　analyzed　in　this　paper.　Research　conclusions:　(1)　The　soil　stress　between　piles　is　increased　and　the　soil　arching　effect　is　weakened　by　dynamic　load.　(2)　Most　of　dynamic　load　is　passed　to　the　top　of　pile　because　of　dynamic　soil　arching　formation.　(3)　The　formation　of　equal　settlement　surface　is　associated　with　the　displacement　arch,　because　the　soil　particles　will　run　into　the　area　between　piles　from　the　area　on　the　top　of　piles　within　the　displacement　arch,　which　leads　to　a　higher　vertical　displacement　on　the　top　of　piles　outside　displacement　arch　and　a　lower　soil　vertical　displacement　between　piles.　(4)　It　will　lower　soil　arch　height　and　weaken　virtual　soil　arches　among　stress　arch　if　the　geogrid　cushion　is　put　into　use,　but　the　pile-soil　stress　ratio　is　increased.　(5)　This　research　results　will　provide　method　of　working　mechanism　for　railway　roadbed　structure.　©　2017,　Editorial　Department　of　Journal　of　Railway　Engineering　Society.　All　right　reserved.