Abstract: The conventional Extended Towed Array Measurement (ETAM) may fail to extend aperture when the Signalto-Noise Ratio (SNR) is not high enough and the phase angle of phase correction factor is close to the discontinuous point. A modified method for estimating phase correction factor is proposed to reduce the instability of the conventional ETAM caused by the discontinuity of cross-correlation phase angle. In this method, the average value of normalized cross-correlation vectors is estimated as the least-square estimation for phase correction factor, which can eliminate the adverse effects caused by discontinuity of the cross-correlation phase angle. Simulation and experimental results show that the proposed method can effectively extend aperture even in the case of a stochastic source, and obtain higher resolution and SNR relative to Conventional Beamforming (CBF). Compared with conventional ETAM, the proposed method has a wider range of applications because the estimation accuracy of phase correction factor and the stability of the algorithm are improved.