We　proposed　a　new　method　for　microwave-induced　thermal　lesion　detection　using　the　autoregressive　spectrum　analysis　of　ultrasonic　backscattered　signals　in　this　paper.　Eighteen　cases　of　microwave　ablation　experiments　and　twenty　cases　of　water　bath　heating　experiments　were　conducted.　Ultrasonic　radiofrequency　data　of　normal　and　coagulated　porcine　liver　tissues　were　collected　through　these　two　experiments.　Then,　autoregressive　spectrum　analysis　was　performed;　the　mean　frequency　of　the　dominant　peak　in　the　autoregressive　spectrum　was　computed　based　on　water　bath　experiments;　and　a　method　for　recognizing　normal　and　solidified　tissues　was　obtained　by　comparing　the　difference　of　the　dominant　peak　in　the　autoregressive　spectrum.　Two　bandpass　finite　impulse　response　filters,　whose　passbands　corresponded　respectively　to　the　dominant　peak　in　the　autoregressive　spectrum　of　normal　and　coagulated　tissues,　were　used　to　compute　the　power　spectral　integration　for　the　microwave-induced　experiments.　Microwave-induced　thermal　lesions　were　detected　based　on　the　differences　between　the　power　spectral　integrations　from　the　two　filters.　Compared　to　the　caliper-measured　area,　the　power　spectral　integration　detected　area　had　an　error　of　(10.25　±　3.59).　Experimental　results　indicated　that　the　proposed　method　may　be　used　in　preliminary　detection　of　microwave-induced　thermal　lesions.　©　2020　by　Begell　House,　Inc.