Cold knees at night may be caused by environmental factors such as cold, but also rheumatoid arthritis, lower extremity vascular disease and other pathological factors. 1. Environmental factors: may be due to the indoor temperature is relatively low, or sleep at night did not cover the quilt, resulting in the knee joint parts of the soft tissue spasm, the feeling of cold knees, and may cause calf cramps and other phenomena. 2. Rheumatoid arthritis: a rheumatic immune disease, often because the knee area is subjected to long-term cold or bacterial attack produces a kind of inflammatory reaction, which will lead to abnormal changes in the blood supply to the knee area, feel the knee area cold, the night will be more obvious. 3. Lower extremity vascular disease: mostly seen in the lower extremity venous thrombosis, which will lead to poor blood circulation in the lower extremities, feel the knee cold when sleeping. At night, cold knees must pay attention to the warmth of the knee area, if the symptoms persist, it is recommended that patients go to the hospital in a timely manner to identify the causes of standardized treatment.