CPR can greatly improve the survival rate of patients as an emergency treatment to be performed for blood circulation of cardiac arrest patients. Since the experience and skill of the person performing the CPR affects the survival rate of the patient, a method capable of measuring the quality of CPR needs to be developed. In this study, when CPR is executed, it is trying to confirm the blood flow induced by external chest compression by defining the mechanical impedance based on the compression force and the compression velocity of the patient's chest. Through a program designed with LabVIEW, the measured data is extracted for only one period at 100 BPM to obtain the amplitude and phase, and the mechanical impedance is defined. Using the mechanical impedance value according to the presence or absence of blood flow, we can obtain an index to detect blood flow during CPR. It is expected that the mechanical impedance of the chest during CPR can be confirmed in real time and it can be used to judge the quality of CPR using impedance according to blood flow.