Endoscopic ultrasonography (internal ultrasound) plays an important role in the diagnosis and treatment of digestive diseases. Endo-ultrasound is a means of imaging and cannot replace histological diagnosis. The application of endo-ultrasound-guided fine needle aspiration has made histopathologic diagnosis possible. In this paper, we briefly introduce the clinical application and safety of EUS-FNA based on literature reports and our application experience. 1. Performance characteristics of EUS-FNA Both linear and rotational internal ultrasound scanning modes can be used for guided fine-needle aspiration. Because the scanning plane of linear endoscopy is parallel to the long axis of the endoscope, the direction and line of the puncture needle is continuously revealed in the field of view, and its color Doppler function can detect the important vessels around the lesion, which is extremely helpful to reduce puncture complications. Gress et al. compared two types of scan-guided fine-needle aspiration in pancreatic lesions and suggested that it is better to apply line-array scanning endoscopy because it is safer and easier to master. 2, Safety of EUS-FNA The basic conditions for EUS-FNA are ① direct visualization of the lesion on ultrasound scan; ② clear needle path; ③ no blood vessels at the puncture site; ④ no coagulation disorder and bleeding tendency of the patient. Contraindications: ① moderate amount of ascites or more, systemic weakness that cannot tolerate endoscopy; ② serious bleeding tendency; ③ acute inflammation at the puncture site; ④ high mental stress and uncooperative. Statistics from the literature show that the average complication rate of EUS-FNA is about 1.5%. The complications include pancreatic pseudocyst bleeding, fever, perforation, and complications of acute pancreatitis, which are usually not serious and can be cured by conservative treatment or surgery. barawi et al. performed blood cultures on 100 patients 30 and 60 minutes after puncture and followed up for 1 week, and all the blood cultures were negative, and none of the cases had fever. 3. Clinical significance of EUS-FNA Internal ultrasound has a high detection rate for gastrointestinal, mediastinal and pancreatic diseases. Although imaging features such as inhomogeneous hypoechoic masses can help in the determination of malignant lesions, they still cannot distinguish their benign and malignant nature very reliably. The diagnosis of enlarged lymph nodes around the upper gastrointestinal tract also lacks specificity based only on the size and morphology of the lymph nodes and their echogenic intensity. EUS-FNA can obtain sufficient specimen content to provide a definitive histological and cytological diagnosis, and is therefore of great importance for clinical management. Bhutani et al. reported 47 cases of suspected pancreatic cancer due to painless obstructive jaundice or epigastric pain with weight loss, who underwent EUS-FNA after finding a mass shadow on EUS. The sensitivity, specificity, positive predictive value, and negative predictive value for pancreatic tumors were 64%, 100%, 100%, and 16%, respectively. similar results were reported by Gress et al. and Sahai et al. The combined use of EUS and EUS-FNA not only allows for early detection of tumors, clarifying their benignity and malignancy, and determining the presence of lymph node metastases, but also has important implications for clinical staging of patients, development of individualized clinical treatment plans, and determination of prognosis. In the report of Chang et al. 27% of patients avoided surgery, 57% avoided more intensive investigations or treatment, and 68% changed their original treatment plan. In recent years, with its increasing clinical application, EUS-FNA has evolved from a purely diagnostic technique to a therapeutic tool, such as endo-ultrasound-guided intraesophageal wall botulinum toxin injection for the treatment of primary pancreatic dystonia, alcohol injection into the abdominal plexus for pain relief in cancer pain and chronic pancreatitis, and aspiration therapy for pseudopancreatic cysts. There are also recent reports of internal ultrasound-guided injection of various cytotoxic substances directly into the pancreatic tumor for the treatment of pancreatic cancer. Overall, EUS-FNA is continuing to develop its clinical applications, and we look forward to its further achievements in the diagnosis and treatment of clinical diseases.