Purpose: To study and analyze the causes of low back pain caused by lower extremity causes. Low back pain caused by lower extremity disorders is often not taken seriously, and a little carelessness can lead to misdiagnosis and mismanagement, which can cause great pain to both the doctor and the patient. Some low back pain disappears after successful lower extremity joint replacement surgery; while others occur after inappropriate joint surgery. METHODS: The author found that some patients had a combination of lower back pain of varying degrees through the consultation of a large number of hip and knee replacement patients. By studying the relationship between lower back pain and lower extremity pain, we can achieve the purpose of proper diagnosis and treatment. I found that some cases combined with lower back pain through systematic analysis of a large number of cases of artificial hip and knee joint replacement, which were analyzed systematically to find out the causes. The results: 1. the patients’ low back pain was entirely triggered by lower limb disorders (e.g. day-old acetabular dysplasia, resulting in lower back pain); 2. low back pain and lower limb pain coexisted, and the symptoms of low back pain were aggravated by lower limb pain or functional limitation; 3. it was from medical source of lower back pain. These cases are caused by improper hip or knee replacement surgery, resulting in lower limb inequality or lower limb functional limitation, which triggers lower back pain. Conclusion: In the diagnosis and treatment of low back pain and lower limb conditions, the two should be organically combined to find out the root of the lesion, and careful preoperative examination and accurate intraoperative operation can avoid the occurrence of lower limb-derived low back pain in order to avoid misdiagnosis and mistreatment.