The causes of knee joint effusion are as follows: 1. Inflammatory factors and diseases such as hemophilia, rheumatism and rheumatoid can lead to knee joint effusion, and etiological treatment is recommended; 2. Trauma may lead to synovial bleeding or cartilage damage, resulting in knee joint effusion; 3. Normal joint cartilage has a certain degree of degeneration, resulting in wear and tear of cartilage debris during limb activities, which may stimulate the synovial membrane, resulting in increased secretion and decreased absorption of synovial membrane, further leading to knee joint effusion, which can be treated by reducing activity and local physical therapy.