To　study　the　effect　of　large　blood　vessels　on　the　temperature　field　in　invasive　microwave　ablation,　a　finite　element　method　was　applied　based　on　the　convective-type　boundary　condition　on　the　interface　between　tissues　and　blood　flow.　Whether　a　large　blood　vessel　is　outside　of　or　involved　in　the　lesion　area　will　affect　the　54　degrees　C　effective　therapeutic　area　in　different　critical　conditions.　This　paper　drew　the　function　diagraph　on　the　distance　between　blood　vessel　and　antenna　with　the　diameter　of　the　blood　vessel　and　put　forward　the　concept　of　effective　therapy　radius.　It　can　be　used　to　study　the　influence　of　large　vessels　on　the　external　boundary　of　the　coagulation　area　and　can　be　used　as　a　theoretical　basis　to　help　to　decide　whether　to　occlude　the　large　vessels　before　microwave　ablation　therapy.