Abstract: For the issue of the bad Direction Of Arrival (DOA) estimation accuracy entailed by not utilizing the transmitted polarization information in electromagnetic vector sensor MIMO radar, a transmitted polarization optimization algorithm is proposed based on minimizing the Cramr-Rao Bound (CRB). First, the signal model of electromagnetic vector sensor MIMO radar for DOA estimation is proposed. Second, the drawbacks of the existing fixed polarization DOA estimation algorithm are analyzed. Third, the CRB under arbitrary polarization is derived and the polarization state corresponding to the minimum CRB is computed. Finally, with the optimal polarization, the DOA can be estimated by the fixed polarization DOA estimation algorithm. The proposed algorithm can provide better estimation accuracy than the fixed polarization DOA estimation algorithm, and remain the advantages of automatic pairing between the two dimensional DOA estimation and arbitrary placement of the transmitted electromagnetic vector sensor antennas. Simulation results verify the effectiveness of the proposed algorithm.