It　is　critical　for　microwave　ablation　(MWA)　treatment　planning　to　evaluate　the　changes　of　thermal　coagulation　zones.　In　MWA　procedures,　the　shapes　and　sizes　of　thermal　coagulation　zones　are　gradually　evolving　over　time.　To　this　end,　a　novel　characterization　and　mapping　method　of　thermal　coagulation　zones　is　presented　in　this　article.　Firstly,　finite　element　method　(FEM)　models　of　temperature　distributions　for　40,　45,　50,　55,　and　60W　microwave　ablations　were　built　to　derive　thermal　ablation　data　of　ex　vivo　porcine　livers　and　were　compared　with　experimental　results.　Secondly,　growth　models　of　characteristic　lengths　were　fitted.　Finally,　characterization　functions　of　thermal　coagulation　zones　were　developed　using　these　growth　models.　In　addition,　shape　variation　factors　were　incorporated　to　handle　the　minor　shape　variations　of　thermal　coagulation　zones.　Experimental　results　showed　that　these　characterization　functions　could　accurately　represent　the　changes　of　thermal　coagulation　zones.　The　standard　deviations　between　prediction　results　and　simulated　values　were　less　than　1　mm.　The　comparative　results　were　statistically　analyzed　by　paired　t　test　(P＞0.05),　indicating　no　significant　differences.　The　proposed　method　can　simply　and　effectively　predict　the　changes　of　MWA　coagulation　zones　with　time,　thus　providing　reliable　coagulation　dimensions　for　the　thermal　ablation　therapies.