Objective: To evaluate the safety, feasibility and clinical efficacy of transthoracic single-hole assisted laparoscopic radical gastrectomy for Siewert Type Ⅱ adenocarcinoma of esophagogastric junction. Methods: A prospective, single-center, one-arm study will be performed. Patients who have been diagnosed with Siewert type Ⅱ esophagogastric junction adenocarcinoma and meet the eligibility criteria will be included in the study and undergo the transthoracic single-hole assisted laparoscopic radical gastrectomy. The data of preoperative, intraoperative, postoperative and follow-up will be recorded and analyzed. Primary study endpoints: The incidences of early postoperative complications and mortality. The secondary study endpoints:(1) Surgery and oncology indicators ;(2) Early postoperative recovery information ;(3) 3-year disease-free survival and overall survival rate;(4) 5-year disease-free survival and overall survival.