The filtering of the data collected by ECG, QRS detection and wavelength measurement can greatly shorten the time for doctors to find abnormal waveforms in a large number of ECG waveforms and improve their working efficiency. In this paper, a realtime ECG QRS detection method based on the differential zero-crossing detection method is proposed. First, the baseline deviation and high- frequency interference of the original signal are filtered out, and then the QRS features are extracted from the signal through the steps of difference and nonlinear mapping. The experiment proves that this method is suitable for practical application.