Patients develop joint cavity effusion, and the main site of predilection is in the patient’s knee joint area. This is due to the aging, degeneration and hyperplasia of the knee joint bones, resulting in osteoarthritis and synovitis, which can produce joint effusion. If the patient has a small amount of fluid in the knee cavity and only feels pain in the knee joint area, it does not affect normal walking or knee flexion and extension functions and is not clinically serious. In this case, no special treatment is needed, but the patient should be instructed to reduce activities and apply local pressure bandages. If the patient has more fluid in the knee cavity, more local swelling, positive floating patella test, and the pain increases when the patient puts weight on the knee, it affects the knee flexion. In this case, symptomatic treatment can be given by aspirating the joint fluid and applying a compression bandage. Alternatively, sodium vitreous acid can be injected into the knee joint to nourish the cartilage and synovial membrane, which can reduce the effusion of joint fluid.