A new algorithm based on one single snapshot is proposed for the instantaneity and decorrelation problems among Direction-Of-Arrival (DOA) estimation of signals on a ULA, which reconstructs a Toeplitz matrix using the correlation processed data vector. It is proved that the rank of this Toeplitz matrix has no relations with the coherency of the signals. Then accurate signal subspace and noise subspace can be acquired by performing eigenvalue decomposition of the matrix and the DOA of coherent and incoherent signals can be estimated combined with the subspace kind algorithms such as MUSIC and ESPRIT. This algorithm, without reducing the aperture of array, enhances the performances of DOA estimation under low SNR condition. Simulation results verify that the proposed algorithm is effective.