Objective To explore the application of magnetic resonance imaging (MRI) in the diagnosis and treatment of lacunar infarction in order to provide a reference for clinical diagnosis of this disease. Methods The clinical data of 80 patients with lacunar infarction admitted to our hospital from July 2013 to July 2018 were retrospectively analyzed. All patients were given X-ray computed tomography(CT) and MRI after admission. And the two examination results were compared and analyzed. All patients were given MRI again after 1 month of treatment, and the results were compared with MRI results before treatment. Results Among 80 patients with lacunar infarction, 751 lesions were detected by MRI, and 156 lesions were detected by CT, and the detection rate of MRI in frontal lobe was significantly higher than that of CT(P<0.05), and the detection rates in internal capsule and cerebellum were significantly lower than those of CT(P<0.05). The detection rate of MRI for lesions≤5mm was significantly higher than that of CT(P<0.05), and the detection rate for 6-10mm lesions was significantly lower than that of CT(P<0.05). The lesions in all patients were reduced after 1 month of treatment, and the lesions≥11 mm were significantly reduced compared with first MRI examination(P<0.05), and the lesions≤10 mm were not significantly different from the results of first MRI examination (P>0.05). Conclusion Compared with CT, MRI has a higher detection rate for lacunar infarction, and it is clear for small lesions, and it is conducive to the differential diagnosis of diseases.