Tumor recurrence and metastasis after liver transplantation is the most common problem and an important factor affecting patients’ survival. It is believed that the main reason for recurrence and metastasis of liver cancer after liver transplantation is the microcirculatory metastases or cancer thrombi within the portal vein system after surgery, and the hematogenous extrahepatic dissemination caused by tumor cells shedding through portal vein. Meanwhile, the use of immunosuppressive drugs, which is indispensable after liver transplantation, further accelerates the growth and spread of tumor. Currently, there is no definitive and effective method to treat these recurrent and metastatic tumor lesions. Although hepatic artery chemoembolization (TACE), radiotherapy (RT) and radiofrequency ablation (RFA) are effective for recurrence and metastasis of liver cancer after liver transplantation, they are invasive and prone to various comorbidities. Compared with the above treatment methods, high intensity focused ultrasound (HIFU), also known as HEFU, is a nearly non-invasive treatment method that has been applied in the treatment of various benign and malignant tumors such as uterine fibroids, benign and malignant breast tumors, liver cancer, pancreatic cancer and retroperitoneal tumors. Its treatment principle mainly includes: ①Thermal effect: the focused ultrasound beam of HIFU can reach a high sound intensity at the focal point, so that the sound energy is rapidly absorbed by the tissue and converted into heat energy, resulting in a high temperature of 65 ℃ or more in a local instant. ②Mechanical effect. The high frequency oscillation of the molecular structure of the tissue cells in the body subjected to ultrasound, the mechanical effect of strong changes, i.e., mechanical effect, causes cell lysis, functional changes, degradation of DNA macromolecules and protein denaturation, and can cause the reduction of intercellular adhesion coefficient, causing cell separation and detachment. ③ cavitation effect. When the ultrasound intensity is high, the sound pressure amplitude is large, and the positive and negative pressure alternate, the tiny bubbles inside the tissue compress and expand under the effect of this positive and negative pressure and rupture, causing energy release and instantaneous increase in local temperature and lead to cell necrosis. Moreover, HIFU treatment does not damage the surrounding normal tissues, which is a non-invasive and effective means of treating tumors and some non-tumor diseases with great potential. It can “excise” the tumor completely and achieve the effect of local surgical resection without the complications of traditional surgery (such as bleeding, blood loss, infection, wound scar formation, etc.), and can be repeatedly treated. At the same time, HIFU treatment also has good immunomodulatory effects.