A method for extracting foetal ECG from combined maternal and foetal ECG measured using abdominal electrodes uses a separation vector, and is based on the relative sparse characteristic of the source signal in time domain. A plurality of mixed mother-fetus electrocardio signals from different positions on the abdomen of a mother are collected and pre-processed. Two of the mixed signals are selected using maximum SNR, and positions of QRS wave groups of the maternal ECG and fetal ECG are determined to identify relatively sparse periods of the electrocardiograms where the QRS groups of the maternal ECG and FECG do not overlap. The relatively sparse periods are converted to a time-frequency domain using an ambiguity function, and signal items and cross items in each time-frequency distribution are calculated. A control function is constructed based on general Rayleigh quotient to separate the maternal and fetal signals.
