Objective To measure brain atrophy in patients with subcortical ischemic vascular disease (SIVD) by a linear method, and to analyze its correlation with cognitive impairment. Methods A total of 50 patients were assigned to SIVD group and 50 healthy volunteers to control group. For all the subjects, general state of health was evaluated; cognitive function was assessed by Montreal Cognition Assessment (MoCA); the brain was examined by magnetic resonance imaging; brain atrophy was measured by a linear method. Results All the measured values of cerebral ventricular transverse diameter and sulcus were significantly larger in the SIVD group than in the control group except for the width of pontine cistern (P<0.05). All the measured relative values of brain atrophy were significantly larger in the SIVD group than in the control group except for the brainstem index (P<0.05). In the SIVD group, the maximum distance between the two foreheads of both lateral ventricles, the minimum distance between the caudate nuclei near the two foreheads of both lateral ventricles, the width of the third ventricle of the brain, and the minimum distance between the pars lateralis of both lateral ventricles were negatively correlated with the MoCA score (P<0.05); some measured relative values of brain atrophy, i.e., forehead angle index, caudate nucleus index, Huckman's value, and width of the third ventricle of the brain, were negatively correlated with visual space, computational ability, delayed memory, and spatial orientation ability (P<0.05). Conclusions The patients with SIVD have substantial cortical and subcortical atrophy, which are closely related to cognitive impairment. Hashimoto's value, forehead angle index, caudate nucleus index, and width of the third ventricle of the brain can be used as predictors of brain atrophy and indicate the impairment of executive function/visual space, computational ability, and memory.