The　existence　of　large　blood　vessels　seriously　impacts　the　results　of　microwave　ablation　on　heat　transfer　of　surrounding　tissue,　and　the　research　of　influences　about　large　blood　vessels　could　be　essential　and　significant.　The　temperature　distribution　in　the　tissue　was　analyzed　with　a　microwave　heating　source　by　finite　element　method.　The　model,　where　the　blood　vessel　is　parallel　to　antenna,　has　different　distances　from　antenna　to　blood　vessel.　As　distance　was　greater　than　20mm,　the　effect　of　blood　vessel　that　was　parallel　to　antenna　was　ignored　and　the　ablation　area　was　elliptical-like.　When　distance　was　less　than　lOmm,　the　part　of　asymmetrical　coagulated　area　was　on　the　right　side　of　blood　vessel.　Therefore,　the　temperature　contour　by　different　conditions　could　provide　numerical　references,　which　is　whether　to　block　blood　vessel　or　not,　to　achieve　the　aim　of　guiding　the　clinical　practice,　according　to　the　locations　of　tumor　and　blood　vessel.