Thyroid cells are very active in growth and metabolism, and localized abnormal growth can form one or more tissue masses known as thyroid nodules. Thyroid nodules are becoming more common with the popularity of physical examinations and the widespread use of ultrasound and other imaging tests. The prevalence of thyroid nodules obtained by touch in adults is 3% to 7%, while the prevalence of thyroid nodules obtained by ultrasound examination is as high as 20% to 76%, but fortunately the majority of these nodules are benign and malignant nodules, i.e. thyroid cancer, account for only a minority of them, about 5% to 15%. Benign nodules usually do not require surgery, but only regular follow-up, while malignant nodules require surgery to remove them, so it is important to distinguish between benign and malignant thyroid nodules. Certain ultrasound signs can help distinguish benign from malignant thyroid nodules. Almost all thyroid nodules with the following two types of ultrasound changes are benign: 1) purely cystic nodules; 2) nodules with multiple small vesicles occupying more than 50% of the nodule volume with spongy changes, 99.7% of which are benign. The following ultrasound signs suggest the possibility of thyroid cancer: 1) solid hypoechoic nodules with uneven echogenicity; 2) abundant blood flow in the nodules; 3) irregular nodule shape and margin; 4) calcification in the nodules, especially mud-like microcalcifications; 5) simultaneous abnormal ultrasound images of the cervical lymph nodes. The ability to identify benign and malignant thyroid nodules by ultrasonography is directly related to the clinical experience of the ultrasonographer. Ultrasound results are only an indirect basis for differentiating benign and malignant thyroid nodules. For those who suspect malignancy, it is necessary to use fine needle aspiration under ultrasound guidance and then observe the morphology of the cells under a microscope to obtain direct evidence for differentiating benign and malignant nodules. Fine needle aspiration biopsy of thyroid nodules (FNAB) is simple and less invasive, and its sensitivity and specificity in diagnosing thyroid cancer are 83% and 92%, respectively, and should be used as a routine test and gold standard for preoperative benign-malignant differentiation of thyroid nodules.