Abstract： Objective The value of brain 7T MRI in detecting multiple sclerosis(MS)lesions were compared with 3T MRI recommended by the guidelines.Methods Patients with multiple sclerosis admitted to Beijing Tiantan Hospital Affiliated to Capital Medical University from September 2021 to October2023 were prospec-tively included,and all the enrolled patients met the 2017 revised diagnostic criteria for McDonald MS.Clinical information was collected,and 3T and 7T brain MRI examinations were performed during hospitalization.The 3T and 7T brain MRI sequences included T1WI,T2WI and T2 FLAIR sequences.The 3T and 7T MRI lesions with different locations(cortical,Juxtacortical,periventricular,Infratentorial and atypical lesions in other areas)and diameters were marked and measured respectively,and the differences in the detection of different loca-tions and diameters of lesions were compared between the two kinds of field intensity MRI.Results A total of 12 patients with definite diagnosis of MS were included,with an average age of 32±4.4 years,including 4 males and 8 females.A total of 463 multiple sclerosis lesions(mean lesion diameter:7.2mm)were detected on 7T MRI,and 319 multiple sclerosis lesions(mean lesion diameter:8.8mm)were detected on 3T MRI.The number of lesions detected by 7T MRI were 14,66,194,28 and 161,respectively,in the cortical,Juxtacortical,periventricular,Infratentorial and white matter lesions in other areas.The number of lesions detected by 3T MRI were 8,41,161,25 and 84,respectively.The detection rate of 7T MRI was 42.86％,37.88％,17.01％,10.71％and 47.83％higher than that of 3T MRI,respectively.Within the range of 3mm≤diameter 5mm,5mm＜diameter ≤ 7mm and diameter＞7mm,the number of MS lesions detected by 7T MRI were 173,121 and 169,respectively;The number of MS lesions detected by 3T MRI were 46,106 and 167,respec-tively.The detection rate of 7T MRI was 73.41％,12.40％and 1.18％higher than that of 3T MRI,respective-ly.Conclusion The conventional brain 7T MRI sequence has a higher detection rate for multiple sclerosis le-sions than the 3T MRI sequence under the guidance of guidelines,especially for cortical lesions and lesions within a range of 3mm ≤ diameter≤5mm.Location and diameter were the main reasons for the difference in the detection of multiple sclerosis lesions.