Abstract: In this paper, the effect of signal power on the DOA estimation of incident signals in complex electromagnetic environment is investigated. It is found that the classic evaluation criterion for performance analysis of DOA estimation algorithms has limitations on incident signals with different power. Thus, this paper first demonstrates that the power of strong signal has influence on the DOA estimation performance of weak signal. The increasing of strong signal power will lead to the rising of Cramer-Rao Lower Bound of weak signal, that is, the increasing of the root mean square error. Then this paper analyzes the limitations of the classic evaluation criterion for DOA estimation algorithms in resolving incident signals with different power. Further Monte Carlo experiment results prove that the classic evaluation criterion has a large misjudgment rate for resolving incident signals with different power. When the signal to noise ratio (SNR) of the weak signal is below 5dB, the misjudgment rate of the classic evaluation criterion is higher than 50%. Finally, this paper proposes a new evaluation criterion for DOA estimation algorithm in resolving incident signals with different power. The simulation results indicate that the proposed criterion has better resolution than the classical criterion in dealing with incident signals with different power when the SNR of the weak signal is low. The evaluation criteria proposed in this paper can provide a reference for the performance analysis of DOA estimation algorithm based on spatial spectrum.