Cardiac magnetic resonance cine imaging is more commonly used in clinical imaging method for cardiac function analysis. A real-time free breathing cardiac magnetic resonance cine imaging data processing method, which is an effective way for rapid detection of end-diastolic (ED) and end-systolic (ES) phases at end-expiration graphically, was proposed in this paper. By placing the appropriate reference line in the frames, respiratory motion and cardiac motion could be observed during the entire data collection process of subjects. According to the movements of chest wall/diaphragm and other organs to obtain respiratory motion, the time period of end-expiration could be quickly determined; and then in the time period, cardiac end-diastolic and end-systolic as two important cardiac phases for cardiac function analysis were automatically identified according to the size of the left ventricle chamber. Finally, in accordance with specified requirements, automatically detected images were saved to facilitate subsequent cardiac function analysis. This method significantly reduces data processing time and therefore it has good clinical values and prospects.