The accuracy of locating R wave in ECG signal is the basis of other waveform location, and it is in the primary position in the study of ECG signal characteristic waveform. According to the most obvious characteristic of R wave in the whole ECG waveform, this paper proposes a method to extract R wave based on wavelet theory. First, select an appropriate method to remove the noise from the ECG signal, and then perform 5-layer wavelet decomposition on the denoised ECG signal to obtain approximate signals and detail signals of each order. The average value of the superimposed signal is used as the search threshold, and the search starting point is determined. Finally, map the abscissa of the search starting point to the pure ECG signal, and use the method of comparing the amplitude point by point to search backward, until the R wave is found. Using the data in the MIT-BIH database for multiple experimental verifications, the experimental results show that this algorithm can accurately locate the R wave, and the accuracy of the inspection is 99.65%, the recall rate is 99.86%.