In this paper, a robust algorithm based on spatial differencing matrix is proposed for source number detection and directions-of-arrival (DOAs) estimation of a number of coherent signals simultaneously impinging on the far field of a uniform linear array (ULA). In this proposed approach, the number and DOAs of incident coherent signals can be simultaneously estimated via the eigenvectors of the defined spatial differencing matrix. Compare with the previous works, the proposed method can improve the source number detection and DOA estimation accuracy, as well increase robustness to SNR change.