Left side lumbar pain and leg numbness are mostly caused by lumbar disc herniation, which can cause numbness and pain on one side of the leg when the nerve is compressed by lumbar disc herniation, then CT or MRI examination should be performed to further confirm the diagnosis and treatment. If the leg numbness is diagnosed as a result of lumbar disc herniation, early bed rest is required, usually 1-2 weeks, lumbar traction, oral nerve-nourishing drugs, such as methylcobalamin tablets, vitamin B1 tablets, vitamin B6 tablets, oral pain relief drugs, such as celecoxib and loxoprofen sodium tablets, as well as the treatment of Chinese medicine, such as root pain pellets and lumbar pain capsules. If conservative treatment is not effective, surgical treatment should be considered. If low back pain is accompanied by leg numbness, it can also be caused by a tumor of the nerve root. If it is a syringoma or fibroma of the nerve root, the symptoms of low back pain and leg numbness can occur, and then an MRI is also needed to confirm the diagnosis and treatment.