Objective: To analyze the application value of carotid ultrasound in the evaluation of carotid artery stenosis and prognosis in patients with acute cerebral infarction (ACI). Methods: A total of 102 patients with ACI in Baofeng County Hospital of Traditional Chinese Medicine from August 2022 to August 2025 were enrolled. All patients underwent bilateral carotid ultrasonography within 72 hours of admission. The intima-media thickness (IMT), plaque morphological characteristics (stable/vulnerable plaques) and stenosis degree of the carotid artery on the responsible lesion side were measured. The hemodynamic parameters of the narrowest stenosis site were collected and analyzed. According to the modified Rankin Scale (mRS) score within 90 days after onset, the patients were divided into good prognosis group (mRS≤2 points, 62 cases) and poor prognosis group (mRS>2 points, 40 cases). The clinical data and carotid ultrasound parameters were compared between the two groups. Pearson correlation analysis was used to explore the correlation between National Institutes of Health Stroke Scale (NIHSS) score at admission and carotid ultrasound parameters. Multivariate Logistic regression model was used to screen the independent influencing factors affecting the 90-day poor prognosis in ACI patients. Results: IMT in poor prognosis group was thicker than that in good prognosis group (P<0.05), and the detection rate of vulnerable plaques, proportion of severe stenosis, peak systolic velocity (PSV) and end-diastolic velocity (EDV) of the internal carotid artery in the responsible lesion side were higher than those in good prognosis group (P<0.05). Pearson correlation analysis showed that NIHSS score at admission was positively correlated with IMT, PSV and EDV (P<0.05). Multivariate Logistic regression analysis showed that advanced age, high NIHSS score at admission, presence of severe carotid artery stenosis and presence of vulnerable plaques were independent risk factors of 90-day poor prognosis in ACI patients. Conclusion: Carotid ultrasound parameters are closely related to the neurological deficit degree in patients with ACI at admission. Severe carotid artery stenosis and vulnerable plaques are important indicators for predicting short-term poor prognosis.