Heavy-duty　gantry　machine　plays　an　important　role　in　the　energy,　shipbuilding,　aerospace,　transportation　and　military　industry　and　other　pillar　industries,　and　is　a　manifestation　of　national　equipment　manufacturing　capacity.　Cross　rail　is　one　of　the　key　structural　components,　and　its　natural　frequency　affects　the　dynamic　performance　of　the　machine.　It　is　difficult　to　obtain　the　accurate　analysis　of　natural　frequency　by　using　the　analytical　method　because　of　the　complex　internal　structure.　The　finite　element　method　is　a　general　method　to　obtain　natural　frequency,　but,　is　also　difficult　to　obtain　the　precise　result,　because　the　analysis　result　depends　on　many　factors,　such　as　meshing　manners,　the　constraint　conditions,　joint　parameters,　damping,　and　so　on.　The　density　of　mesh　is　an　important　factor　to　affect　the　analysis　result　especially.　Theoretically,　the　smaller　element,　the　closer　to　the　true　result.　But　more　dense　grid　could　sharply　increase　the　degree　of　freedom,　and　result　in　the　insufferable　solving　speed　in　the　analysis　of　the　cross　rail.　So　to　find　a　balance　point　between　the　speed　and　the　accuracy　becomes　very　meaningful.　In　this　paper,　the　modal　analysis　was　carried　out　on　the　cross　rail.　The　paper　focus　on　exploring　the　influence　of　different　element　size　on　the　results　of　the　analysis.　In　order　to　verify　the　correctness　of　the　modeling,　the　modal　testing　is　carried　on　the　cross　rail,　and　the　experimental　result　is　adopted　to　prove　the　correctness　of　finite　element　modeling.