In this paper, the model of multi-target based on the statistical multiple-input multiple-output (MIMO) radar is analyzed, and the CRLB of multi-target localization estimation in this model is also present. The optimal rule is improved by the thesis of diversity gain and mutual interference based on the CRLB by contrasting the optimal antenna placement within the signal target case. It is shown that the existing inevitability of optimal antenna placement is demonstrated, and the non-symmetrical but horizontal placement is optimal. The performance of the proposed estimator is validated by simulation results.