For neoplastic diseases, pathological histological diagnosis is undoubtedly the most important and in most cases the only way to make a definite diagnosis. However, the difficulty of obtaining lesions for definitive diagnosis varies for different tumors: for tumors located in organs that are connected to the outside world, we can obtain lesions through endoscopic biopsy, such as esophageal, gastric, and colon cancers, we can obtain pathological evidence through general gastroscopy or colonoscopy. However, how do we make pathological diagnosis for most of the tumors in the closed cavity of the body (such as liver cancer, kidney cancer, pancreatic cancer, etc.)? In this case, if there is a high clinical suspicion that the lesion is malignant, doctors often use surgical excision of the lesion to obtain tissue for diagnosis at the same time as treatment. This method has two limitations: firstly, the lesion may be resected and finally diagnosed as not malignant, which makes the organ that could be preserved be removed, and the patient pays unnecessary cost physically, mentally and economically; secondly, although the lesion is malignant, it is advanced and cannot be removed surgically at all, and at this time, it is very costly to open the abdomen or open the chest simply to obtain histological diagnosis. So, is there any simpler and less damaging method to obtain lesion tissue for tumor diagnosis? Endoscopic ultrasound guided fine-needle aspiration (EUS-FNA) is a better solution to the above two challenges. Ultrasound endoscopy is an ultrasound probe built into the front end of a gastrointestinal endoscope, which allows the exploration of lesions in organs outside the GI tract. Fine needle aspiration is performed by inserting a fine needle (about 1 mm in diameter) through the biopsy lumen of the endoscope under the guidance of the ultrasound endoscope to obtain the lesion tissue for diagnosis. With the promotion and development of this technique, fine needle aspiration is not only used for the pathological diagnosis of the primary tumor, but also for the diagnosis of lymph node metastasis or metastasis to other parts of the abdominal cavity, retroperitoneum and mediastinum. Since this method of EUS-FNA is easy (the procedure is like ordinary endoscopy), economical (the cost is much lower than direct vision surgery), less painful to the patient (no pain at all), low incidence of side effects (less than 5%), and quick recovery (complete recovery in 2-3 days), it has been widely used in many fields such as preoperative diagnosis of tumors, assessment of tumor resectability, assessment of chemotherapy regimens before formulation, and determination of tumor recurrence. Although the ultrasound endoscopy-guided puncture technique has many advantages, it is not a panacea, due to the fact that the extent of puncture is limited by the reachable range of the endoscope. At present, the main application areas of EUS-FNA include the diagnosis and differentiation of tumors of the left hepatic, biliary system (gallbladder and bile duct), pancreas, left adrenal gland, bladder and prostate; the presence of lymph node metastasis in gastric, esophageal and rectal cancers; and the determination of the nature of mediastinal, abdominal and retroperitoneal masses. We believe that with the development of endoscopic instruments and techniques, the application of EUS-FNA technology will gradually expand while the incidence of side effects and complications will be further reduced, thus providing a more powerful tool for tumor diagnosis and differentiation.