Aimed at the problems that being caused by deleting the repeated virtual array during DOA estimation, effective information and estimation performance are lost and poor, a symmetric nested MIMO radar DOA estimation algorithm is proposed based on redundancy average of virtual array. Firstly, a set of uniform linear array and a set of sparse uniform linear array are arranged symmetrically by taking zero as a center to constitute a monostatic MultipleInput MultipleOutput radar transmitting array and a receiving array. The array structure is to change the conventional virtual array for a symmetric sum coarray structure from the difference coarray structure, thus increasing the degree of freedom, reducing the mutual coupling of the system, and applying it in uncorrelated and coherent targets DOA estimation. Secondly, the vectorized sample covariance matrix and the Toeplitz matrix are reconstructed by averaging the redundant virtual elements of sumdifference coarray. Finally, the combination of the proposed algorithm with the MUSIC algorithm for DOA estimation effectively improves the performance of target estimation number and angle estimation. The simulation results show that the proposed array structure and algorithm are effective.