Objective：To explore the application value of pulmonary blood flow parameters based on phase contrast magnetic resonance imaging（PC - MRI）in assessing the prognosis of patients with connective tissue disease - associated pulmonary arterial hypertension（CTD - PAH）. Methods：A retrospective analysis was conducted on the clinical data and cardiac magnetic resonance （CMR）parameters of 136 patients with CTD-PAH，as well as the main pulmonary artery（MPA）blood flow parameters measured by PC -MRI. Based on the follow - up results，patients were divided into two groups：the group with clinical deterioration events and the group without clinical deterioration events. The comparison of CMR indicators between the two groups was conducted using either the independent sample t-test or the Mann-Whitney nonparametric test. Independent predictors of endpoint events were screened by Cox proportional hazards regression. Subsequently，patients were grouped based on the optimal cut-off point of the receiver operating characteristic（ROC）curve，and Kaplan-Meier survival analysis was used to verify the prognostic differences. Results：Compared with the group without clinical deterioration events，patients in the group with clinical deterioration events showed decreased left ventricular stroke volume index，left ventricular ejection fraction，right ventricular ejection fraction，left ventricular cardiac index，main pulmonary artery peak velocity，main pulmonary artery mean velocity（MPAMV）. Additionally，they exhibited increased right ventricular end - diastolic volume index（RVEDVI），right ventricular stroke volume index，right ventricular myocardial mass index，and ventricular mass index. These differences were statistically significant（all P ＜ 0.05）. Cox regression analysis indicated that the MPA MV and RVEDVI were independent predictors of clinical deterioration events in patients with CTD-PAH. Kaplan-Meier survival analysis showed that the incidence of clinical deterioration events increased when the MPAMV was ≤6.65 cm/s and the RVEDVI was ≥110.24 mL/m（2 all P ＜ 0.001）. Conclusion：RVEDVI and MPAMV measured by phase contrast sequences are valuable for predicting clinical deterioration events in CTD-PAH patients. Additionally，using both indicators together can further enhance predictive accuracy.