Weakness but no pain in the knee may be caused by physiological factors such as excessive exercise, or it may be caused by pathological factors such as knee ligament injury, knee degenerative disease, hypokalemia, myasthenia gravis and so on, which need to be treated by physical therapy, medication and surgery. 1. Physiological factors: If walking for a long time or exercising excessively will make the muscles and ligaments in a fatigue state, then the symptoms of knee joint softness and weakness without pain will appear, which is a normal physiological phenomenon, and the symptoms can be improved after resting. 2. Knee ligament injury: anterior cruciate ligament or posterior cruciate ligament injury of the knee joint can lead to knee joint instability and weakness and tenderness of the knee joint, and those with minor injuries should be given brakes and rest, and be fixed with casts or braces to protect them, and they can be gradually recovered in 6~8 weeks. 3. Degenerative disease of knee joint: such as cartilage degeneration, subchondral bone edema, weakness and tenderness of knee joint can occur, attention should be paid to rest, avoid weight bearing, long time walking and so on, to protect the wear and tear of the knee joint, oral drugs such as glucosamine can be taken to improve the symptoms of nutritional cartilage. 4. Hypokalemia: Hypokalemia will lead to weakness and numbness of the limbs, and the symptom of weak and feeble knees without pain. Potassium agents such as potassium chloride and potassium citrate can be used under doctor’s guidance. For hypokalemia caused by pituitary adenoma, surgery is needed. 5. Myasthenia gravis: For myasthenia gravis that causes weakness and tenderness in the knees, cholinesterase inhibitors such as neostigmine methylsulfate injection and pyridostigmine are needed under the guidance of doctors. Immunosuppressants such as azathioprine and cyclophosphamide are also available for some patients. There are many other causes of knee weakness but not pain, if the symptoms continue to be unrelieved, the patient should consult a doctor in a timely manner to clarify the cause of the disease and then targeted treatment. The above medications should be used in strict compliance with medical advice.