A patient who has had most of his stomach removed for ulcer disease can, several years later, develop anemia, most commonly iron deficiency anemia. This is a common and easily overlooked disease after surgery. Most gastrectomies are anastomoses of the residual stomach and jejunum, thus ① food cannot pass directly through the duodenum (which is an important place for iron absorption), which affects iron absorption; ② food empties rapidly from the residual stomach and enters the jejunum rapidly, which also affects iron absorption; ③ the stomach secretes gastric acid, and after gastrectomy, gastric acid is significantly reduced or even lacking, which is not conducive to the dissolution, freeing and absorption; ④ the residual gastric anastomosis is prone to superficial inflammation or vesicular bleeding which aggravates anemia. It has been estimated that the average annual decrease in hemoglobin in patients after major gastrectomy is 1% (10 g/L). Therefore, iron deficiency anemia can occur in half of the patients several years after surgery, especially in those who have depleted their preoperative iron stores or are prone to anemia. Iron deficiency anemia that occurs after major gastrectomy can be cured by taking iron for a longer period of time, and the success rate of oral iron has been reported to be 94%. It should be noted that oral iron should be supplemented with dilute hydrochloric acid combination. It can also be treated by intramuscular injection of iron dextran first, and then continue to take oral iron, so that the hemoglobin can rise faster and be easily accepted by the patient. In order to reduce the recurrence of anemia, the inflammation of the residual stomach or anastomosis should also be actively treated, and the body should be supplemented with sufficient amount of iron or replenish the stored iron regularly. In addition, a small number of patients with major gastric resection may have a decrease or lack of endocannabinoids secreted by the gastric mucosa, which may cause megaloblastic anemia, and should be treated with vitamin B12 supplementation.