A front-end measuring system of an automatic external defibullator, an automatic external defibrillator and a measuring method. Firstly, making an analog to digital converter perform the oversampling when the original data is sampled, and then extracting sample values from the oversampled signals respectively according to a set ratio in the subsequent processing, so that one sampling channel can be shared by two or three of the three measuring channels of the impedance , ECG signal and Pace signal of a patient, therefore, the amount of the hardwares in the measuring system is reduced by the front-end measuring system of the automatic external defibrillator, and then the problems of device dispersivity and node interference caused by the large amount of the hardwares are reduced, and the accuracy of measuring result of an instrument id improved.
