To identify the morphological characteristics together with CSF hydrodynamics on preoperative MRI that improve the prediction of foramen magnum decompression (FMD) treatment outcome for Chiari malformations type I (CM-I) patients compared with the CSF hydrodynamics-based model. This retrospective study included CM-I patients who underwent FMD, PC-cine MR, and static MR between January 2018 and March 2022. The relationships of the preoperative CSF hydrodynamic quantifications derived from PC-cine MR and morphological measurements from static MRI, clinical indicators with different outcomes, were analyzed with logistic regression analysis. The outcomes were determined using the Chicago Chiari Outcome Scale (CCOS). The predictive performance was evaluated with ROC, calibration, decision curves, and AUC, NRI, IDI, and compared with CSF hydrodynamics-based model. A total of 27 patients were included. 17 (63%) had improved outcomes, and 10 (37%) had poor outcomes. The peak diastolic velocity (PDV) of the aqueduct midportion (OR, 5.17; 95% CI: 1.08, 24.70; P=0.039) and the fourth ventricle outlet diameter (OR, 7.17; 95% CI: 1.07, 48.16; P=0.043) were predictors of different prognoses. The predictive performance improved significantly than the CSF hydrodynamics-based model. Combined CSF hydrodynamic and static morphologic MR measurements can better predict the response to FMD. A higher peak diastolic velocity (PDV) of the aqueduct midportion and broader fourth ventricle outlet were associated with satisfying outcomes after decompression in CM-I patients.