To　construct　a　reasonable　numerical　model　of　arterial　flow,　the　selection　of　boundary　conditions　in　hemodynamics　was　analyzed,　and　then　the　certain　solution　conditions　were　presented.　Based　on　the　selection,　the　parameters　of　thoracic　aorta　were　employed,　and　numerical　calculations　of　steady　and　unsteady　flows　were　performed.　The　results　indicate　that　boundary　conditions　have　a　significant　effect　on　blood　flow　distributions.