The main reason for feeling swelling inside the knee joint is to consider the increased pressure inside the knee joint, thus producing the feeling of swelling, which may involve the following factors: first, factors related to blood circulation, such as local cold in the knee joint, vasoconstriction or vascular diseases, resulting in obstruction of venous blood return, thus producing blood stasis, resulting in increased local pressure and this symptom; second, then there is fluid in the knee joint, due to acute injury can lead to bloody fluid, due to chronic strain as well as arthritis, synovitis, can lead to inflammatory fluid, the pressure in the knee joint will be increased, producing this swelling sensation; third, can be due to bone lesions in the knee joint, such as bone cysts, bone tumors, can lead to increased pressure in the bone, thus producing a swelling sensation in the knee joint. Patients are advised to go to the hospital for a detailed examination to clarify the diagnosis and actively pursue treatment.