Objective: To evaluate the value of three-dimensional balanced steady state free precession sequence (3D b-SSFP) magnetic resonance imaging (MRI) sequence in diagnosis of anomalous origin of the coronary artery from the pulmonary artery（ACAPA）. Methods: The whole heart MRI3D b-SSFP performed on 21 children with an age of (33.67±43.32) months was retrospectively analyzed. All the subjects had DSA or surgical operation confirmed ACAPA, and 19 cases were isolated heart abnormality. The imaging quality of 3D b-SSFP was evaluated and inter-observer agreement was validated by the Kappa coefficient. Relationship between heart rate and imaging quality was assessed by regression analysis. The diagnostic accuracy of 3D b-SSFP for ACAPA was assessed by comparison with findings from DSA or surgical operation. Results: The subjective scores on the image quality from two observers were 2.84±0.82 and 2.83±0.83, and inter-observer agreement was 81.8% (95% CI 57.0%-86.6%). The heart rate (HR) of investigated subjects was(105.85±18.20) beat/min, and the left ventricular end diastolic volume and ejection fraction were (79.63±37.46) mL/m² and (34.28±21.39)% respectively. Left ventricular late gadolinium enhancement(LGE) was positive in 8 of 10. Regression analysis showed negative correlations between vessel sharpness and HR in both 2 observers, and correlation coefficients were -0.277 and -0.263, respectively. MRI3D b-SSFP identified ACAPA in 18 out of the 21 cases investigated, yielding a diagnostic accuracy of 85.71%. The MRI imaging of 2 cases was beyond recognition due to blurred edge and 1 case was misdiagnosed as normal. Conclusion: Cardiac MRI displays cardiac anatomy and coronary artery and facilitates evaluation of cardiac function. The 3D b-SSFP is a valuable MRI sequence for diagnosing ACAPA.