The causes of double lower limbs swelling in lung metastasis of liver cancer may be reduced albumin, cancer cells invading portal vein affecting venous return and so on. 1. Decrease of albumin: liver is the main organ to produce albumin, which is the main component of vascular osmotic pressure. In liver cancer, liver function is severely damaged, liver cells produce less albumin, and vascular osmotic pressure decreases, resulting in a large amount of water infiltration from blood vessels to tissue interstitial space. Due to gravity, water gathers in the lower part first, so swelling of both lower limbs appears. 2. Cancer cells invade into inferior vena cava: when liver cancer cells invade into inferior vena cava, blood flow from lower limbs to heart will be blocked, resulting in increased pressure in blood vessels, and when the pressure is greater than that in peripheral tissue interstitial space, a large amount of water and small molecules will enter into tissues, resulting in swelling of both lower limbs. When patients with lung metastasis of liver cancer have swelling of both lower limbs, it is recommended to go to regular hospitals in time to clarify the cause of the disease and standardize the treatment, so as not to delay the condition and lose the time of treatment.