Abstract: Aiming at the problem that the performance of the Gerschgorin disks method was degraded when the adjustment factor was set improperly in source number estimation, this paper proposed a modified Gerschgorin disks method based on global least squares fitting. This method kept the radius of the disk as the fitting points of straight line so that the fitting discrepancy of the signal disk radius was much larger than that of the noise disk radius, and a ratio-step criterion was developed to estimate the source number so that no artificial adjustment factor was set. The performance of the TLS-GDE algorithm was verified by simulation. The results show that the robustness of the TLS-GDE is improved and the performance of the TLS-GDE is better than that of the GDE in low SNR.