The main reason for the swelling of the foot during the day and the swelling at night is that when you sleep at night, the affected limb is often elevated, which is conducive to venous return and facilitates the reduction of swelling. During the day, the activity is more, walking is more, the venous return is poorer, there will be swelling, this is the main reason why the feet swell during the day and go down at night. The most common causes of swollen feet are the following: 1. soft tissue damage, fracture, dislocation after foot trauma, local venous channel destruction, poor venous return. 2. kidney problems, such as patients with nephritis, will also cause swollen feet. 3. heart disease, patients with heart failure can also cause swollen feet.