This study semi-quantitatively analyzed the effects of leukoaraiosis. Patients with moderate or severe lacunar infarction were found to exhibit low scores on the Montreal Cognitive Assessment Scale (F = 12.02, P = 0.000), and prolonged P300 Cz2.0 latency (F = 16.04, P = 0.000). Correlation analysis revealed that the occurrence of leukoaraiosis was negatively correlated with Montreal Cognitive Assessment scores (r = -0.416, P = 0.000), and positively correlated with P300 Cz2.0 latency (r = 0.538, P = 0.000). These findings indicate that leukoaraiosis aggravates cognitive impairment in patients with lacunar infarction, such that more severe leukoaraiosis is associated with more severe cognitive decline.