Invasion of the peritoneum by papillary thyroid cancer means the severity of the thyroid cancer lesion, indicating that the thyroid cancer has progressed to the early and middle stages, which is more serious. The thyroid gland is usually in the trachea where the 3rd and 4th cartilaginous rings exist, divided into left and right sides, and the peritoneum is a layer of fascia that surrounds the thyroid gland. When cancerous lesions occur in the thyroid gland, the epithelial cells of the follicles of the thyroid gland undergo lesions, and the normal tissues are destroyed, and they grow and multiply continuously. When papillary thyroid cancer invades to the peritoneum, it indicates that papillary thyroid cancer cells grow faster and gradually approach the surface of the northern thyroid gland, thus invading the peritoneum, the cancer cells are highly invasive and prone to metastasis, which is more serious. When papillary thyroid cancer invades the peritoneum, it is recommended to receive timely surgical treatment under doctor’s guidance to remove the diseased tissue, and then give iodine 131 and other treatments after the surgery and pay attention to review.