Purpose:　The　aim　of　this　study　is　to　investigate　the　effects　of　ablation　parameters　on　thermal　distribution　during　microwave　atrial　fibrillation　catheter　ablation,　such　as　ablation　time,　ablation　power,　blood　condition　and　antenna　placement,　and　give　proper　ablative　parameters　to　realise　transmural　ablation.　Materials　and　methods:　In　this　paper,　simplified　3D　antenna-myocardium-blood　finite　element　method　models　were　built　to　simulate　the　endocardial　ablation　operation.　Thermal　distribution　was　obtained　based　on　the　coupled　electromagnetic-thermal　analysis.　Under　different　antenna　placement　conditions　and　different　microwave　power　inputs　within　60　s,　the　lesion　dimensions　(maximum　depth,　maximum　width)　of　the　ablation　zones　were　analysed.　Results:　The　ablation　width　and　depth　increased　with　the　ablation　time.　The　increase　rate　significantly　slowed　down　after　10　s.　The　maximum　temperature　was　located　in　1　mm　under　the　antenna　tip　when　perpendicular　to　the　endocardium,　while　1.5　mm　away　from　the　antenna　axis　and　26　mm　along　the　antenna　(with　antenna　length　about　30　mm)　in　the　myocardium　when　parallel　to　the　endocardium.　The　maximum　temperature　in　the　ablated　area　decreased　and　the　effective　ablation　area　(with　the　temperature　raised　to　50　degrees　C)　shifted　deeper　into　the　myocardium　due　to　the　blood　cooling.　Conclusion:　The　research　validated　that　the　microwave　antenna　can　provide　continuous　long　and　linear　lesions　for　the　treatment　of　atrial　fibrillation.　The　dimensions　of　the　created　lesion　widths　were　all　larger　than　those　of　the　depths.　It　is　easy　for　the　microwave　antenna　to　produce　transmural　lesions　for　an　atrial　wall　thickness　of　2-6　mm　by　adjusting　the　applied　power　and　ablation　time.