Objective：To investigate guideline adherence to preventive pharmacotherapy in patients with migraine，quantify the extent of undertreatment and potential overtreatment，and analyze the associated influencing factors. Methods：In this cross-sectional study，2 028 patients with migraine who attended the specialized headache clinic of the First Affiliated Hospital of Nanjing Medical University between January 2020 and August 2025 and fulfilled the diagnostic criteria of the International Classification of Headache Disorders，3rd edition（ICHD-3）were enrolled. According to the Chinese Guidelines for the Diagnosis and Treatment of Migraine（2023 edition）and the International Headache Society’s global practice recommendations for preventive pharmacological treatment of migraine，≥4 monthly migraine days was defined as the indication for preventive treatment. Based on treatment indications and actual medication use，patients were categorized into four groups：indication - comforming group（Group A），potential overtreatment group （Group B），appropriate acute treatment group（Group C），and inappropriate medication use group（Group D）. Clinical characteristics and medication patterns were compared among the groups. Multivariable logistic regression was performed to identify factors associated with undertreatment in Group A. Results：Among the 2 028 patients，685（33.8%）were assigned to Group A，of whom 21.2%（145/685） were undertreated. Groups B，C，and D comprised 446（22.0%），619（30.5%），and 278（13.7%）patients，respectively. Preventive medications in Groups A and B were mainly calcium channel blockers and antiepileptic drugs，with a significantly higher use of calcium channel blockers in Group B than in Group A（71.3% vs. 40.6%，P ＜ 0.001）. For acute medications，triptans，acetaminophen， nonsteroidal anti-inflammatory drugs，and calcitonin gene-related peptide receptor antagonists were used most frequently in Group C. Multivariable logistic regression showed that the use of acute migraine-specific medications（adjusted OR=1.90，95%CI：1.27-2.82，P= 0.002）and a greater number of monthly migraine days（adjusted OR=1.02，95%CI：1.00-1.03，P=0.036）were significantly associated with undertreatment in Group A. Conclusion：Preventive treatment of migraine demonstrated a clear pattern of bidirectional nonadherence，characterized by undertreatment among patients with indications for preventive therapy and potential overtreatment among those without such indications. In clinical practice，stricter adherence to indications for preventive treatment is needed，along with strengthened evaluation of preventive therapy among users of migraine - specific acute medications and more standardized drug selection and headache subtype diagnosis，in order to improve guideline adherence.