Leg swelling in bone metastasis of lung adenocarcinoma may be caused by hypoproteinemia, poor local blood flow or thrombus. Lung adenocarcinoma is of high malignant degree, with the continuous development of adenocarcinoma, it will consume a large amount of nutrients in the body, which may cause hypoproteinemia, and at this time, if bone metastasis occurs, leg swelling may occur due to low plasma osmotic pressure. When bone metastasis occurs in lung adenocarcinoma, local metastatic tumor tissues may press surrounding blood vessels leading to poor blood return, which will also cause leg swelling. When bone metastasis of lung adenocarcinoma leads to poor blood return, blood clots, mostly venous blood clots, may be considered to be treated by thrombolysis or placing filters. If lung adenocarcinoma with bone metastasis has swollen legs, on one hand, regular radiotherapy should be carried out to inhibit the continuous growth of tumor, on the other hand, attention should be paid to actively replenish proteins and other nutrients, and proper treatment should be carried out under the guidance of doctors.