The invention belongs to the field of radar signal processing, and discloses a limb motion separation method based on radar principle component analysis. The method comprises: obtaining an Lx1 dimensional echo signal of monopulse radar, using a moving window in length of K to observe the echo signal for N times, to obtain an NxK dimensional observed signal matrix, wherein N is observation times, K is length of the moving window, that is, the number of sampling points, and N is far smaller than K; using the NxK dimensional observed signal matrix as a sampling space covariance matrix, calculating the characteristic value of the sampling space covariance matrix, according to the observation frequency N, the length K of the moving window, and the characteristic value, calculating characteristic dimensionality of the echo signal; using principle component analysis PCA to reduce dimensionality of the sampling space covariance matrix, to decompose the sampling space covariance matrix into principle components in the same number with the characteristic dimensionality; and clustering the plurality of principle components, so as to separate the plurality of principle components.