In recent years, the incidence of esophagogastric junction cancer has increased year by year. It is a special type of gastric cancer, with 80% of patients being clinically in the middle and late stages. The traditional treatment methods are extremely ineffective, and the accuracy of preoperative staging is not good enough. At present, the medical treatment for esophagogastric junction cancer mainly adopts surgery and postoperative adjuvant therapy. The current mainstream clinical diagnostic methods of esophagogastric junction cancer before concurrent neoadjuvant chemoradiotherapy are X-ray, CT examination, and gastroscopic diagnosis. However, these clinical diagnostic methods have many limitations. Endoscopic ultrasonography (EUS) can accurately locate malignant tumors in the digestive tract, surrounding microstructures. It can diagnose lymphatic metastasis so as to provide a clear imaging basis for neoadjuvant chemoradiotherapy. This method can also effectively improve the prognosis of the esophagus and stomach according to the characteristics of the patient. In this experiment, we conducted a controlled trial on patients with stage III esophagogastric junction cancer, divided into an experimental group (neoadjuvant chemotherapy + surgery) and a control group (conventional surgery). The preoperative EUS staging in the control group, the preoperative EUS staging in the neoadjuvant chemoradiotherapy group, and the postoperative pathological staging were compared. The experiment showed that in the control group, the preoperative and postoperative accuracy of EUS was 89.2%, while the preoperative and postoperative accuracy of CT examination was only 62.5%. In the experimental group, the preoperative and postoperative accuracies of EUS and CT were 79.6% and 56.7%, respectively. EUS has both specificity and accuracy due to CT examination. Through studying EUS technology in the staging and diagnosis of esophagogastric junction cancer, the therapeutic effect of esophagogastric junction cancer can be improved. The prognosis of esophagogastric junction cancer can also be improved.