Objective To investigate the dynamic ultrasonographic characteristics of the ablation areas of solid thyroid nodules after microwave ablation. Methods A total of 434 nodules of 364 patients treated with ultrasound-guided percutaneous microwave ablation in The Second Affiliated Hospital of Naval Medical University (Second Military Medical University) and Shanghai International Medical Center from Jan. 2015 to Dec. 2018 were selected, including 329 in benign nodule ablation group and 105 in malignant nodule (thyroid papillary carcinoma) ablation group. All nodules were completely ablated. The ultrasonographic features (including the echo, peripheral acoustic halo, needle tract, calcification, aspect ratio, boundary and the change of the color Doppler flow) of the ablation areas of the 2 groups at 1, 3, 6 and 12 months after ablation were analyzed retrospectively, and the similarities and differences between the 2 groups were summarized. At the same time, the ultrasonic images of the 105 nodules in the malignant nodule ablation group were collected before ablation. The ultrasonic characteristics of the nodule ablation areas in the 2 groups were compared with those of malignant nodules before ablation, so as to explore their similar characteristics and key points for differentiation. Results The ablation areas of the benign and malignant thyroid nodules showed hypoechoic echo with needle tract and hypoechoic acoustic halo after ablation, with no internal blood flow signal. The ablation needle tracts of 20 nodules were absorbed 12 months after operation, and the other needle tracts showed an absorption trend over time. The acoustic halo was incomplete at 1 month after operation, was complete and clear at 3 months, and was gradually blurred at 6 and 12 months. The clearest boundary was found at 3 and 6 months after operation, but blurred at 1 and 12 months. There was no blood flow signal in the ablation areas from 1 to 12 months after operation. The ablation areas with calcification generally aggregated at 3 months after operation, and the aggregation became more obvious over time. Before the ablation, papillary thyroid carcinoma showed solid hypoecho, unclear boundary, coarse margin, incomplete acoustic halo and scattered microcalcification, with internal and peripheral blood supply, which were similar to the characteristics of ablation areas in the benign and malignant nodule ablation groups at all time points. Conclusion The ultrasonographic features of benign and malignant thyroid nodules in the ablation areas are consistent, and some of the ultrasonographic features are similar to those of papillary thyroid carcinoma without ablation, but they can be identified by needle tract, acoustic halo, calcification distribution and blood supply in the ablation areas.