Background　Unclippable　fusiform　basilar　trunk　aneurysm　is　a　formidable　condition　for　surgical　treatment.　The　aim　of　this　study　was　to　establish　a　computational　model　and　to　investigate　the　hemodynamic　characteristics　in　a　fusiform　basilar　trunk　aneurysm.　Methods　The　three-dimensional　digital　model　of　a　fusiform　basilar　trunk　aneurysm　was　constructed　using　MIMICS,　ANSYS　and　CFX　software.　Different　hemodynamic　modalities　and　border　conditions　were　assigned　to　the　model.　Thirty　points　were　selected　randomly　on　the　wall　and　within　the　aneurysm.　Wall　total　pressure　(WTP),　wall　shear　stress　(WSS),　and　blood　flow　velocity　of　each　point　were　calculated　and　hemodynamic　status　was　compared　between　different　modalities.　Results　The　quantitative　average　values　of　the　30　points　on　the　wall　and　within　the　aneurysm　were　obtained　by　computational　calculation　point　by　point.　The　velocity　and　WSS　in　modalities　A　and　B　were　different　from　those　of　the　remaining　5　modalities;　and　the　WTP　in　modalities　A,　E　and　F　were　higher　than　those　of　the　remaining　4　modalities.　Conclusions　The　digital　model　of　a　fusiform　basilar　artery　aneurysm　is　feasible　and　reliable.　This　model　could　provide　some　important　information　to　clinical　treatment　options.　Chin　Med　J　2012;125(1):97-101