Abstract: In this paper, an approach of eigen-analysis for DS-SS signals under narrow band (multiple tone) interference is proposed, which can estimate the PN (Pseudo Noise) sequence blindly in the low SNR(Signal Noise Ratio) and SIR(Signal Interference Ratio) DS-SS signals. Of course, the parameters of the DS-SS signals (such as period and chip interval of the PN sequence) need to be known. Firstly, the received signal is divided into a lot of non-overlapping temporal vectors according to the period of PN sequence, and then the correlation matrix of the vectors is calculated and accumulated. The eigenvalue decomposition of the matrixes can be computed and the narrow band interference waveforms and the PN sequences of the received signals from the main component eigenvectors can be blindly estimated in the end. Based on the estimated narrow band interference waveforms and PN sequences, the narrow band interference can be rejected, and the DS-SS signals despreading without the PN code can be realized too. Theoretic analysis and experimental results show that the approach is very effective. It can work well on the lower SNR and SIR ambient.