Lower back pain when lying down but not when standing up can be caused by the following reasons: 1. Tumor of spine, when there is tumor of spine, there can be nocturnal resting pain when sleeping, which is a pain characteristic of tumor. This is a pain characteristic of tumor. At this time, we should check the MRI, CT of spine and blood test of tumor series for early diagnosis and treatment; 2. Osteoporosis, serious osteoporosis can lead to pain at spine when lying down, and there can be lumbar pain, at this time, we should check lumbar vertebrae’s X-ray film, CT, and blood test for diagnosis in early stage, and we should go to endocrinology department to find out the cause of osteoporosis if necessary; 3. Serious myofasciitis and lumbar strain. Lumbar muscle strain, these two diseases can also have the symptom of lower back pain at night when sleeping and no pain when standing. At this time, it is necessary to examine and early checkup to exclude other diseases for early diagnosis and treatment.