Cerebrospinal fluid examination is an important auxiliary means for diagnosing MS: about 95% of MS patients in western countries can detect abnormalities of OCB and Ig intrathecal synthesis rate, while 5% of negative patients cannot be easily diagnosed with MS, and need to be closely followed up and observed; in China, there is a 66-75% positive rate of OCB in patients, and therefore the other 25% of negative patients with MRI and VEP, SEP, etc. are often considered as CDMS when combined with the clinical characteristics. Combined with the clinical characteristics of highly supportive patients, CDMS is often considered. OCB is not an absolute specific indicator, many other diseases such as vasculitis, tumor damage to the blood-brain barrier, cerebral parasitosis and so on, patients can also appear OCB positive or weakly positive. OCB is more sensitive than MRI in the diagnosis of MS, especially in patients with only some signs and symptoms of MS, for example, cerebrospinal fluid OCB can predict the occurrence of CDMS in patients with optic neuritis, but it is not an independent predictor, and needs to be analyzed in conjunction with MRI. However, it is not an independent predictor and needs to be analyzed in conjunction with MRI.