In order to solve the problem of the effective aperture loss and resolution reduction of the direction of arrival (DOA) estimation algorithm under the coprime array due to the use of spatial smoothing preprocessing, a matrix with overlapped and augmented coarray preprocessing method is proposed. The principle of this method is to split the spatial smoothing covariance matrix and make use of the characteristic of its submatrices of having the same signal subspace. Overlap processing was applied to submatrices and the number of rows of the covariance matrix was expanded, thereby increasing the effective aperture. The simulation results validated that the proposed method can improve the resolution of the DOA estimation, and the accuracy of the estimation is also improved at low snapshots. At the same time, Unitary Estimation of Signal Parameter via Rotational Invariance Techniques (U-ESPRIT) algorithm was applied to the coprime array. By using matrix overlap preprocessing and combining U-ESPRIT algorithm, the DOA estimation result is more accurate than traditional methods.