Aiming at the problem that the heartbeat signal is easily interfered by respiratory harmonics and other noises and difficult to extract, a vital sign detection algorithm based on N peak capture is proposed. First, the radar signal received by the average cancellation method to filter out static clutter, and it uses the range gate selection algorithm to extract the body surface vibration signal; then it performs low-pass filtering and autocorrelation processing on the body surface vibration signal to remove random noise. On the basis of extracting the breathing frequency, its higher harmonics are suppressed, and M peak frequencies are captured in the heartbeat frequency band, then the peak frequency of the maximum number of occurrences of the heartbeat frequency band is calculated iteratively N times as the heartbeat frequency. Simulation results show that the algorithm has higher measurement accuracy and better anti-interference ability than the discrete Fourier transform (DFT) algorithm, and can be effectively used in the field of vital signs detection.